First, sift (or push through metal strainer) the cocoa powder to get all of the lumps out.
Mix in sugar and flour, baking powder, baking soda and salt. Wisk well.
Add eggs, milk, oil and vanilla. Mix well, the batter will be very thick.
Last, add the boiling water. After mixing, the batter will now be very thin.
Pour into 2 9 inch rounds (greased and floured), 1 9x13 (greased and floured) or about 26 standard sized cupcakes with paper liners. With this thin batter, its about 1/4 cup of batter per cup. (Or, 2 full muffin pans and another small sized something for the extra).
Bake at 350. 30-35 minutes for cakes and 20-25 minutes for cupcakes.
These don't rise to be very large and puffy. They have a flat top, perfect for frosting.