Preparing Angel Food Cake Batter:

1. Separate the eggs: Carefully separate the egg whites from the yolks. It’s crucial that no yolk gets into the whites, as this will prevent them from whipping properly. For best results, separate eggs while cold, then let the whites come to room temperature.

2. Sift dry ingredients: Combine cake flour, half the sugar, and cream of tartar. Sift this mixture several times to aerate the ingredients and remove any lumps.

3. Beat egg whites: In a clean, grease-free bowl, beat egg whites on medium speed until foamy. Add cream of tartar and continue beating.

4. Add sugar gradually: Slowly add the remaining sugar while beating, allowing time for it to dissolve. Beat until stiff, glossy peaks form—the mixture should hold its shape when you lift the beaters.

5. Fold in flour: Gently fold the sifted dry ingredients into the egg whites in three additions. Be careful not to overmix, as this will deflate the batter.

Preparing Yellow Sponge Cake Batter:

1. Preheat oven and prepare pan: Start by preheating your oven to the temperature specified in the recipe (usually around 350°F/175°C). Grease and flour a cake pan, typically a round or square pan.

2. Combine dry ingredients: Whisk together the cake flour, baking powder, and a pinch of salt.

3. Cream butter and sugar: In a separate bowl, use an electric mixer to beat together softened butter and sugar until light and fluffy.

4. Beat in egg yolks: Add egg yolks one at a time, beating well after each addition. Stir in vanilla extract and any desired citrus zest.

5. Alternate wet and dry ingredients: Gradually add the dry flour mixture to the wet ingredients in three additions, alternating with milk in two additions. Begin and end with the dry ingredients. Mix just until combined—don’t overbeat.

6. Pour into pan: Spread the yellow sponge batter evenly into your prepared cake pan.