In a large bowl, and butter and sugar and cream together with a mixer until fluffy. Add eggs in, one at a time, beating well after each one. Add in the vanilla and beat together.
In a medium bowl, whisk the flour, cocoa, baking soda, and salt together. IN another bowl, combine the water and butter milk together.
Add the dry ingredients alternately with the buttermilk in thirds to the butter mixture, mixing well with the mixer after each addition.
Line muffin tins with cupcake liners. This will make 24 cupcakes. Fill each 2/3 full with batter.
Bake at 375 degrees for 15-20 minutes until a toothpick inserted into the center of one on the middle cupcakes comes out clean.
Cool in the tins for 10 minutes, then remove to a cooling rack to cool completely.
For the frosting, add the butter and powdered sugar to a large bowl. Beat together with a mixer until smooth. Add in the melted chocolate and vanilla. Beat until smooth and then use to frost the cooled cupcakes. Sprinkle with chocolate sprinkles. Makes 2 dozen cupcakes.