Grapefruit Poppy Seed Cake

5 from 18 votes

Tender and fluffy poppy seed cake layers with grapefruit curd and cream cheese frosting.

Course: Dessert

Cuisine: Cake

Keyword: Grapefruit Poppy Seed 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

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.

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).

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.

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.

Serving: 20g