8 large eggs, separated
8 ounces castor sugar
12 ounces unsalted butter
1½ cup all-purpose flour
1½ teaspoons baking powder
1½ teaspoons pure vanilla extract
2 tablespoons good quality cocoa powder
¼ teaspoon salt
½ teaspoon orange zest
Preheat oven at 350°F with a wire rack in the middle.
Line an 8-inch round cake tin with parchment, butter and flour.
Sift flour, baking powder and salt in a bowl.
Cream butter in the bowl of a stand mixer fitted with the paddle attachment till light and fluffy.
In a separate bowl, whisk the egg yolks with the sugar till light.
Gradually add this into the butter and beat on medium speed till just incorporated.
In a separate bowl, with a hand mixer, whisk the egg whites till stiff peaks form.
With a spatula, fold in the meringue into the egg yolk mixture in 3-4 batches.
Add in the dry ingredients gradually until just incorporated.
Divide the batter into two, ¾ in one batch and the rest in another bowl.
Add the orange zest into the larger batch.
Then sieve cocoa powder over the lesser batch and fold to mix well.
Pour batter into tin, alternating between the two mixtures, starting with the yellow batter and
ending with the cocoa mixture.
Rap pan on counter several times to eliminate air bubbles.
Swirl around the batter with a long skewer to create the marble effect.
Bake for 40-55 minutes or until a tester inserted into the middle of the cake come out clean.
Adapted from sugareverythingnice