Grapefruit Poppy Seed Cake

Jan 06

Tender grapefruit  poppy seed cake, layered with grapefruit curd and cream cheese frosting.

I’m not sure about you, but after that dark chocolate peanut butter cake, I was in need of something light and fruity! I’ve had this grapefruit poppy seed cake on my mind for a while and am so excited I finally had a chance to try it out. This cake originates from a lemon poppy seed cake that I found several years ago and have made nearly a dozen times. The cake and the frosting from the original recipe are light and fluffy, and full of flavor. I have nothing against the original recipe and for a lemon poppy seed cake, it’s my go-to. I simply had the thought to try this cake with grapefruit instead of the lemon, and then add a grapefruit curd since they’re in season and I’m obsessed. Sometimes my ideas are crazy and don’t work out, but this one… it’s a winner!

This cake is really simple to make and can definitely be done in steps. I made the grapefruit curd the day before and stored it in my refrigerator until I was ready to use it. I then made the cake layers the next morning and put it all together later that night. If you’re not going to eat it right away, make sure to cover it in an airtight container and put it in the refrigerator over night. Then let it come back to room temperature before serving.

A quick note about the curd: the color of the grapefruit curd is going to change with each step of the cooking process. When the grapefruit juice is added to the sugar and cornstarch, you get the true grapefruit pink color.

However, once you add your egg yolks, the curd will turn a deep yellow color, like lemon curd. You can certainly use the curd just like this if you want.

If you’d rather the color of the curd better resemble the inside of a grapefruit, just add a little food coloring. I used just a little pink gel and got a vibrant coral color.

As for the vanilla bean, here’s a look at how to cut it open and extract the seeds: slice the vanilla bean down the center and pull apart the two sides to expose the seeds. Use the side of the knife to scrape out the seeds and add it to the ingredients. (Your hands are going to smell amazing after this step!)

I really love how the color of the curd turned out and how it stands out against the white cake and frosting. If you don’t love grapefruit, you can go back to the original recipe and use lemon zest and lemon juice in place of the grapefruit. I’ve also made the original lemon poppy seed cake without curd and it’s fabulous. You really can’t go wrong with this cake.


Grapefruit Poppy Seed Cake

Yield 1 3-layer, 8-inch cake

Tender grapefruit  poppy seed cake, layered with grapefruit curd and cream cheese frosting.


For the Grapefruit Curd (recipe source: Cookie Dough and Oven Mitt)

  • 6 egg yolks
  • 1 cup sugar
  • Zest from 1 grapefruit
  • 1/4 teaspoon salt
  • 1/4 cup cornstarch
  • 2 cups grapefruit juice
  • 3 tablespoons unsalted butter, cold

For the Grapefruit Poppyseed Cake (recipe adapted from: Technicolor Kitchen)

  • 3 cups cake flour
  • 1 3/4 cups granulated sugar, divided
  • 4 1/2 teaspoons baking powder
  • 1/2 teaspoon salt
  • 3 tablespoons poppy seeds
  • 1 cup (2 sticks) unsalted butter, room temperature, coarsely chopped
  • Grated zest and juice of 1 large grapefruit
  • 1 1/4 cup buttermilk
  • 5 egg whites

For the Vanilla Cream Cheese Frosting (recipe source: Technicolor Kitchen)

  • 2 vanilla beans
  • 5 cups confectioners' sugar, sifted
  • 8 ounces cream cheese, room temperature
  • 1 cup (2 sticks) unsalted butter, room temperature
  • 1 tablespoon pure vanilla extract


For the Grapefruit Curd

  1. In two bowls, divide the egg whites and yolks. Set aside the egg whites for another recipe.
  2. Add the zest of one large grapefruit in with the egg yolks and mix briefly.
  3. In a medium saucepan, add the sugar, salt and cornstarch and whisk until combined.
  4. 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.
  5. Once it comes to a boil, let it boil for 2 minutes, whisking constantly to avoid burning.
  6. Slowing pour about 1/2 cup of the juice mixture into the egg yolks that you've set aside, whisking while you pour. Continue whisking to avoid the yolks from cooking. This is tempering the yolks.
  7. Add the tempered yolks into the saucepan with the juice and whisk until incorporated.
  8. Let the grapefruit curd come up to a boil and boil for about 5 minutes, until thickened.
  9. Remove from heat and add the cold butter. Whisk until the butter is melted and well combined.
  10. 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 Grapefruit Poppyseed Cake

  1. Preheat the oven to 350 degrees F. Butter or spray three 8-inch round cake pans and line the bottoms with parchment paper. Butter or spray the paper.
  2. Combine the flour, 1 1/2 cups sugar, baking powder, salt and poppy seeds in the large bowl of a stand mixer fitted with the paddle attachment. Beat on low speed to blend the ingredients and break up any lumps, about 30 seconds.
  3. Add the butter, grapefruit zest and 1 cup of the buttermilk to the flour mixture. Beat on low until completely mixed, then raise the speed to medium and beat for two minutes to lighten and aerate the batter.
  4. In a medium bowl, combine the egg whites with the remaining 1/4 cup buttermilk and whisk to blend thoroughly. Add this mixture to the batter in 2-3 additions, scraping down the sides of the bowl and beating only enough to incorporate. Divide the batter among the prepared pans.
  5. Bake for 23-25 minutes (mine were done at 24 minutes, so keep an eye on them around 20 minutes). Let the cakes cool in the pans for 10 minutes.
  6. While the cakes are cooling, make the grapefruit syrup: in a small saucepan, combine the remaining 1/4 cup sugar and grapefruit juice. Bring to a boil, stirring to dissolve the sugar.
  7. Turn the cake layers onto wire racks and gently poke holes on the top of each cake layer with a toothpick. Generously brush each cake layer with the grapefruit syrup. Let cool completely.

For the Vanilla Cream Cheese Frosting

  1. Split the vanilla beans lengthwise and scrape the seeds into the sugar with the back of a knife.
  2. 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. Gradually add in the 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 and beat well.


  1. Place one cake layer, bottom side down, on a cake plate and pipe a rim of frosting around the edge of the cake layer to create a barrier for the curd.
  2. Evenly spread about 2/3 cup of the grapefruit curd on the cake layer.
  3. Repeat with the second cake layer, another boarder of frosting and 2/3 cup curd.
  4. Place the final cake layer, top side down, on top. Give the cake a quick crumb coat and chill for 20-30 minutes in the refrigerator or 10-15 minutes in the freezer before frosting the entire cake.

5 thoughts on “Grapefruit Poppy Seed Cake

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  1. Hello there from Germany, I was looking for a Grapefruit Curd filled Cake and found your amazing Page. The recipe sounds great, but I have question to the cake preparation, I cant find how much of the sugar goes in für cake batter and how much in the Grapefruit syrup… Could you please help me out here?! Thanks in advance – Lisa

  2. I only use 9 inch pans, how much would you say to multiply by to do 3 9 inch layers? 1.5? Or would it work to just use this as 2 9 inch layers?