Citrus Surprise Grapefruit Cake
- Preheat the oven to 350°F Lightly grease two 9" round cake pans, line with parchment, and lightly grease the parchment. Set aside.
- Whisk together the flour, baking powder, and salt in a medium bowl; set aside.
- Combine the egg yolks and oil. Beat at low speed, using your stand mixer or a hand mixer. Slowly add the sugar as the mixture thickens. Add the water and grapefruit juice. Beat on medium speed for 3 minutes, stopping occasionally to scrape the bottom and sides of the bowl. Gently fold in the flour mixture and grapefruit zest with a wide rubber spatula.
- In a separate bowl, free of any oil or grease, beat the egg whites until foamy. Add the cream of tartar and continue to beat on high speed until soft peaks form.
- Gently fold the beaten whites into the batter by thirds. Combine only until traces of white remain; don't over-mix.
- Divide the cake batter between the two pans and bake for 20 to 25 minutes, until a cake tester tests clean and the cake begins to pull away from the sides of the pan. For a 9" x 13" pan, bake 25 to 35 minutes. For cupcakes, bake 15 to 18 minutes.
- Cool in the pan for 10 minutes before turning out onto a rack to cool completely. Frost as desired; cream cheese frosting and Italian buttercream both work well.