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Grapefruit Poppy Seed Cake – tender and fluffy poppy seed cake layers with a grapefruit curd and cream cheese frosting.
Grapefruit Poppy Seed Cake
Time for another cake update! This Grapefruit Poppy Seed Cake has been on the blog for nearly four years and was in serious need of a makeover. And I’m not just talking pictures. The cake itself was super yummy, but after several more years of practicing and learning more about cakes, I knew it could be even better.
Poppy Seed Cake
The first set of changes I knew I needed to make were in the cake layers. While I liked the flavor and texture of the cake, I received comments and emails that some people struggled with getting a moist cake from this recipe. I’ll write another post about how to make sure you get moist cakes, but with this one, aside from watching the bake time, I knew that using all egg whites and the poppy seeds could be causing an issue.
When we only use egg whites in a cake, we risk getting a dry cake because there’s no fat from the yolks to help create moisture. However, sometimes we don’t want to add yolks because we want to keep the cake layers nice and white. So, we need to add fat somewhere else. Similar to my Champagne Cake, I ended up adding a cup of sour cream to this cake batter to ensure a super moist cake.
I had also read, after posting my initial recipe, that poppy seeds absorb moisture and can be a reason a poppy seed cake doesn’t taste moist. To make sure this doesn’t happen, you’ll just soak your poppy seeds in water for about 5 minutes. After they’re soaked, strain the excess water and mix them into the batter as instructed.
But, above all else, making sure you don’t over bake your cake layers is the sure-fire way to make sure you don’t end up with a dry cake. Keep your eye on your cake layers toward the end of the bake time. And remember, when you insert a toothpick in the center of the cake, it SHOULD come out with a few moist crumbs on it.
Next up, the grapefruit curd. Have you ever made grapefruit curd? It sounds like most people haven’t, but I’m about to change your world. If you love a lemon or citrus curd of any kind, you’ll love this tart, sweet grapefruit curd.
Making homemade curd is incredibly simple. You’ll start by mixing sugar, corn starch and salt in a sauce pan. After those dry ingredients are mixed well, you’ll then add the grapefruit juice and begin to cook the mixture over medium heat. As the mixture cooks, it will thicken a bit. When this happens, it’s time to add the egg yolks. The key here is to make sure you temper the eggs so we don’t cook them into scrambled eggs when we add the hot juice mixture. In the instructions you’ll notice that we take out a little of the hot juice and add it to the yolks while stirring quickly. After we’ve tempered the eggs like this, we can then add the egg mixture into the juice mixture and continue to cook. You’ll finish up the curd by adding butter and straining it through a mesh strainer.
The curd is a great element to make ahead of time. You can store it in the fridge in an airtight container for a couple weeks.
TIP: for a true grapefruit color, add a bit of “soft pink” Americolor food gel to the curd at the end of the cooking process.
Cream Cheese Frosting
The cream cheese frosting on this cake creates an awesome culmination of flavors: sweet, tart and tangy!
I don’t use a ton of cream cheese in my cream cheese frosting because I think it can become too overpowering. Instead, I use just 4 ounces of cream cheese to give the buttercream a tangy flavor without it stealing the show.
As you’re planning out the elements of this cake, here’s how I’d lay out the week:
- Three days before you want to serve the cake, make the grapefruit curd. You’ll store the curd in an airtight container in the fridge until you’re ready to use it.
- Two days before you want to serve the cake, make the cake layers. Once the layers are cooled, wrap each one in plastic wrap and freeze. Remove the layers from the freezer about an hour before you plan to stack and decorate the cake.
- The day before you want to serve the cake, make the frosting. Once complete, store in an airtight container and refrigerate.
- The day you plan to serve the cake, remove the frosting from the fridge a couple hours before you want to stack and decorate. Rebeat the frosting for a few minutes and then begin assembly.
Grapefruit Poppy Seed Cake
Tender and fluffy poppy seed cake layers with grapefruit curd and cream cheese frosting.
FOR THE CAKE
- 1 cup (226 g) unsalted butter room temperature
- 1 3/4 cups (350 g) granulated sugar
- 6 egg whites room temperature, (save three yolks for the curd)
- 1 cup (240 g) sour cream room temperature
- 1 tsp. (5 g) vanilla extract
- 3 cups (345 g) cake flour
- 1 tbsp. (10 g) baking powder
- 1 tsp. (5 g) salt
- 1 cup (230 g) grapefruit juice I used fresh squeezed
- 3 tbsp. (27 g) poppy seeds soak in water for a few minutes, strain and then dry off with a paper towel
FOR THE GRAPEFRUIT CURD
- 3 yolks (save the egg whites for the cake)
- 1/2 cup (100 g) sugar
- 2 tbsp. (16 g) corn starch sifted
- 1 cup (230 g) grapefruit juice I used fresh squeezed
- 2 tbsp. (28 g) unsalted butter cold
- 1 drop Soft Pink Americolor Food Gel optional
FOR THE FROSTING
- 1 1/2 cups (339 g) unsalted butter slightly chilled
- 4 oz. cream cheese slightly chilled
- 6 cups (750 g) powdered sugar measured and then sifted
- 3 tbsp. (42 g) heavy whipping cream
- 1 tsp. (4 g) vanilla extract
- pinch of salt
- *This buttercream recipe makes enough to fill and cover your cake. If you want to add additional piping, you’ll want to make an extra 1/2 batch.
FOR THE CAKE
- Preheat your oven to 325 degrees F. Spray three 8-inch or four 6-inch round cake pans with nonstick spray, line the bottom with parchment paper and spray again. Set aside.
- In a medium sized mixing bowl, whisk together the cake flour, baking powder, salt and poppy seeds. Set aside.
- In the bowl of an electric mixer, fitted with the paddle attachment, cream the butter and the sugar for two minutes on medium-high speed.
- Scrape down the sides of the bowl and begin to add the egg whites on medium speed, scraping down the sides and bottom of the bowl between addition.
- Add the sour cream and beat until incorporated, about one minute.
- With the mixer on low speed, add 1/3 of the flour mixture, followed by 1/2 cup of the grapefruit juice. Repeat the additions, 1/3 cup flour mixture, 1/2 cup juice and the final 1/3 cup flour mixture. Add the vanilla. Only mix until the flour mixture is incorporated, about 30 seconds. Scrape down the sides and bottom of the bowl and mix again for another 20 to 30 seconds on low.
- Pour about 18 ounces of cake batter into each of the three 8-inch cake pans or 12 ounces in each of the 6-inch pans and bake for 28-30 minutes - until a toothpick inserted into the center of the cake comes out with a few moist crumbs on it. Let cool in the pans for about 15 minutes and then invert onto a wire rack to cool completely. (Tip: spray your wire cooling racks with nonstick spray).
FOR THE CURD
- In a medium saucepan, add the sugar and cornstarch and whisk until combined.
- Add in the grapefruit juice and whisk until incorporated into the sugar mixture. Place the saucepan over medium heat and let it come up to a boil. Whisking occasionally.
- Once it comes to a boil, let it boil for 2 minutes, whisking constantly to avoid burning.
- Slowing pour about 1/2 cup of the juice mixture into the egg yolks that you've set aside, whisking while you pour to avoid the eggs cooking. This is how to temper your yolks.
- Add the tempered yolks into the saucepan with the juice and whisk until incorporated.
- Let the grapefruit curd come up to a boil and boil for about 5 minutes, until thickened.
- Remove from heat and add the cold butter. Whisk until the butter is melted and well combined. Strain the curd through a mesh strainer.
- Place in a shallow dish and cover with plastic wrap. Be sure that the plastic wrap is touching the curd, otherwise it may form a skin. Let set in the refrigerator 2-3 hours. Can be made several days in advance of the cake.
FOR THE BUTTERCREAM
- In a large bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese and butter on medium speed until light and fluffy.
- With the mixer on low speed, gradually add in the powdered sugar, 1 cup at a time, beating well after each addition and scraping down the sides of the bowl. Continue to beat until very fluffy, about 3-4 minutes.
- Add the vanilla extract, pinch of salt and heavy cream. Continue to beat the mixture for about 3 to 5 minutes, until light and fluffy.
- NOTE: This type of buttercream is a bit "sticky" because of the cream cheese, which makes it hard to get really smooth sides. I recommend using a more rustic design instead.
- Place one cake layer, top side up, on a cake board or cake plate. Frost the top of the layer with about 1/2 cup to 2/3 cup buttercream. Pipe a rim of frosting around the edge of the cake layer to create a barrier for the curd.
- Evenly spread about 1/4 cup to 1/3 cup of the grapefruit curd over the buttercream. Be careful not to overfill the cake layer with curd. If you use too much curd between layers, it's likely to ooze out the side of your cake and make your cake wobbly as you decorate. Stick with a small amount between layers and reserve the rest of the curd to serve a spoonful with each slice of cake.
- Repeat these steps with a second layer of cake and more filling.
- Place the final cake layer, top side down, on top. Apply a thin layer of frosting around the entire cake and then freeze for 10 to 15 minutes. This is the crumb coat. The crumb coat ensures that you don't have crumbs in your final coat of frosting.
- After the crumb coat is set, continue to frost the cake with the remaining buttercream.