In a large workbowl, combine butter and sugar. Slowly drizzle in the beaten eggs, beat well. In a separate bowl combine the instant coffee and milk. Add vanilla and salt. Stir in the cocoa powder sifted together with the baking powder. Finaly add in the flour. The mixture should be black and thick.
Put the dough in the refridgerator to rest for at least one hour.
Preheat oven to 350 degrees F.
Scoop out dough and roll into 1" balls. Press each ball into a 1/2" thick disk. Bake for 10-15 minutes, until edges are just firm.
Cookies can be baked as is or can be rolled in powdered sugar.