Preheat oven 350 F

Beat egg yolks, butter, and icing sugar until fluffy and smooth

On a separate bowl (which as you can see I used pan hahaha), beat egg whites until stiff

On a separate bowl, mix flour and baking powder

Stir/fold in milk a little at a time, alternating with egg white

Lastly, stir/fold in beaten egg yolks

Divide batter into two, add cocoa powder to one

By tablespoon, drop each batter one after another, making a marble effect, into greased and floured bundt pan (unless your pan/mold is silicone/nonstick)

Bake until knife/skewer/toothpick inserted comes out clean (45-55 minutes)

Cool on rack