Grapefruit Layer Cake with Grapefruit Curd and Vanilla Mascarpone Frosting

In the midst of winter’s many customary gingerbread and apple and pumpkin desserts, it can be nice to change it up a bit. And happily, good grapefruits are easiest to get in New York at this time of year. I made this cake for afternoon tea and it was ideal because it’s a light and citrus-y, perfect to pair with a nice Earl Grey or even a jasmine green tea.

The first time I tried this recipe I made it with a grapefruit buttercream to complete the grapefruit trifecta, but it was much too sugary and might even possibly have been too much of a good thing. The vanilla mascarpone frosting has a pleasing sourness from the mascarpone, but also helps play up the delicious grapefruit flavor in the curd which is really the star of the show.

I strongly recommend making the curd and the cakes the night before you plan to serve them and then assembling them all day of. The cake actually can get a little bit stronger of a flavor the second day, which makes it even better.

Grapefruit Layer Cake with Grapefruit Curd and Vanilla Mascarpone Frosting

Adapted from Sugar Hero

Grapefruit Cake
7 oz (1 cup) granulated sugar
Zest of 1 large grapefruit
4 oz unsalted butter, at room temperature
2 eggs, at room temperature
¼ cup fresh grapefruit juice
6 oz (1.5 cups) cake flour
1 ¼ tsp baking powder
a pinch of salt
4 oz (.5 cup) buttermilk, at room temperature

  1. Preheat the oven to 350 F and line two 6″ pans with parchment paper. Place the sugar and grapefruit zest in the bowl of a large stand mixer. Rub them together with your fingers until the sugar is moist and very fragrant. Add the room temperature butter and beat them together with a paddle attachment until light and fluffy, about 3-5 minutes.
  2. Scrape down the sides and bottom of the bowl, then with the mixer running, add the eggs one at a time, beating well after each addition. Add the grapefruit juice and mix it in.
  3. In a separate bowl sift together the cake flour, baking powder, and salt. Add a third of the dry ingredients, then when they’re mostly mixed in, add half the buttermilk and mix it in. Continue to alternate adding wet and dry ingredients, ending with the drys. Stop the mixer when most of the flour streaks have disappeared, and finish mixing by hand, being sure to scrape the bottom and sides of the bowl well.
  4. Divide the batter between the pans. Bake the cakes for 20 minutes, rotating halfway through, until the tops spring back when lightly pressed and a toothpick inserted into the center comes out clean. Cool the cakes on a wire rack for 20 minutes before turning them out and letting them cool completely.
Grapefruit Curd

2 tsp unflavored gelatin powder (optional, see Note below)
2 tbsp cold water
4 oz unsalted butter, at room temperature
10½ oz (1½ cups) granulated sugar
3 eggs
3 egg yolks
1 cup fresh grapefruit juice
2 tbsp fresh lemon juice
Pink and orange food coloring

  1. Make the curd at least 4 hours in advance. (The curd can be made up to a week in advance and kept in the refrigerator until ready to use.) In a small bowl, combine the gelatin and cold water and whisk together. Set aside to let the gelatin absorb the water while you prepare the rest of the recipe.
  2. Fill the bottom of a double boiler (or a regular saucepan) with about an inch of water and bring it to a simmer on the stovetop.
  3. In a large mixing bowl, cream together the butter and the sugar with a handheld or stand mixer fitted with a whisk attachment until the mixture is light and fluffy. Slowly add the eggs and yolks, and beat for 1 minute more. Add the grapefruit and lemon juices and mix—at this point the mixture will look curdled.
  4. Pour the liquid into the top of a double boiler or a bowl that fits snugly over your saucepan. (I actually like to use the metal mixing bowl that goes on my stand mixer so I’m not dirtying too many dishes.) Cook the mixture over the simmering water, whisking frequently, until it thickens enough to coat the back of a spoon. If you want to use a candy thermometer, cook the curd until it reaches 175 degrees F. This process might take 10-20 minutes, depending on the equipment you’re using.
  5. Once the curd thickens, remove the pan from the heat and add the gelatin. Whisk until the gelatin liquefies and everything is well-mixed. Add a few drops of pink food coloring and one drop of orange, to make a nice grapefruit color. Pour the curd through a fine mesh strainer into a bowl to remove any bits of cooked egg. Press a layer of cling wrap directly on top of the curd, and refrigerate it until it is chilled and thick.
Mascarpone Frosting
8 oz mascarpone
200ml heavy cream
3/4 cup icing sugar
1 tbsp vanilla
1 tsp milk powder
Whip cream in bowl of standing mixer. Move into medium bowl and set aside (no need to clean bowl of standing mixer). Mix mascarpone, sugar, vanilla and milk powder in standing mixer with paddle attachment. Fold whipped cream into mascarpone mixture delicately, making sure to deflate cream as little as possible.
Assembly
With a serrated knife, gently cut the dome off the top of each layer and then split them in half to make 4 layers. Fill a piping bag fitted with a star tip with frosting. Place the first layer on a plate or cake stand, using a small amount of frosting to keep it in place. Pipe around the edge of the layer. Spread the grapefruit curd inside the piped circle. Repeat with remaining layers. Pipe frosting around the entire top layer.

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