Preheat the oven to 350°F. Grease and flour two 9-inch round cake pans, three 8-inch round pans, or a 13 x 9-inch sheet cake pan.
In a large mixing bowl, cream together the butter, sugar and salt till fluffy and light, beating for at least 5 minutes. In a separate bowl, whisk together the flour, cocoa and baking powder. If lumps remain, sift the mixture.
Add the eggs to the butter mixture one at a time, beating well after each addition. Mix together the milk or water and the vanilla. Add one-third of the flour mixture to the creamed mixture, then add half the milk, another third of the flour, the remainin
Bake the cake(s) in a preheated 350°F oven for 30 to 35 minutes (a bit longer for the sheet cake), until a cake tester inserted into the center comes out clean, and the cake begins to pull away from the sides of the pan. Remove the cake(s) from the oven,