Preheat oven to 350 degrees.

Heat the butter, water and cocoa until the butter is melted and the ingredients are very hot.  The mixture doesn’t need to come to a boil.  This can be done in a saucepan on the stovetop or in the microwave.

Combine the flour, sugar, baking soda and salt; add to cocoa mixture. Stir in the buttermilk, vanilla and beaten eggs.

Mix by hand or at low speed with a hand mixer until smooth (do not overmix).

Pour into greased 10″ x 15″ cookie sheet and bake for 20-25  minutes, until a toothpick inserted in the center comes out clean.

Cut into circle shape matching the size of your spring form pan.