1. Beat eggs and sugar until light and foamy.
2. Sift together flour, baking powder, and vanilla. Add to eggs, alternating with orange juice and oil. Add cocoa if desired.
3. For best results, set aside batter for one hour before filling cups.
4. Fill measuring cup with batter and pour into lined cupcake tins, 2/3 full. Bake at 350 degrees Fahrenheit for 20-25 minutes.