Preheat oven to 350. Grease and flour two 8-inch round cake pans.
In a mixing bowl, stir together the cake flour, baking powder, baking soda, and salt. Set aside.
Using a stand-mixer fitted with the paddle attachment, beat the butter on low. Add the sugar and increase the speed to medium. Beat until fluffy, 3-4 minutes. Add one egg at a time, beating well after each addition. Add the citrus juices and zest, beating together until combined (the mixture will appear somewhat curdled at this point).
Add the flour mixture in three additions, alternating with the buttermilk, beginning and ending with the flour, scraping down the bowl as necessary. Mix on low until just combined.
Divide batter evenly between the two prepared cake pans and spread flat with an offset spatula.
Bake 25-28 minutes. Cool completely and fill with citrus curd (recipe below) and frost with cream cheese icing.
In the bowl of a stand-mixer fitted with the paddle attachment, cream the butter until fluffy. Gradually add the powdered sugar on a low speed, increasing speed after the powdered sugar is incorporated. Add the citrus zests and beat to combine. For stiffer frosting, add another 1/4-1/2 cup powdered sugar as desired.
In a saucepan, whisk together the eggs and sugar until well combined. Whisk in the citrus juices and zest. Turn the heat on to medium-low and stir the mixture briskly and constantly until warmed through. Add the butter a little at a time until it melts into the mixture and becomes smooth. Continue cooking and stirring until the curd begins to thicken and coat the spoon. Refrigerate the curd in an airtight container until ready to use as filling for citrus cake with cream cheese frosting. Any leftover curd can be kept in the refrigerator for up to a week and used on biscuits or scones.
Decorator’s note: I piped a thick circle of the cream cheese frosting around the top perimeter of the bottom cake layer before spreading the citrus curd onto the cake. This helped prevent the curd from oozing out of the center of the cake when I frosted it.