In a medium saucepan, melt butter and brown sugar.
Remove from heat and cool slightly before adding eggs, one at a time.
Add coffee and vanilla and mix well.
Combine the flour, cocoa, baking powder and salt; add to sugar mixture and mix well.
Stir in chocolate.
Spread into a lightly greased 13" x 9" baking pan.
Bake at 350° for 25-30 minutes and a toothpick inserted in the center comes out mostly clean.