Preheat oven to 350 degrees F. Liberally coat a 9-inch X 13-inch pan with baking spray.

Melt butter, chocolate and sugar in double boiler or a heat proof bowl set over a post of simmering water.  Let cool. In a separate bowl whisk together the flour, baking powder and salt. Add the eggs, and remaining dry ingredients to the melted butter/chocolate/sugar mixture. Mix together until well blended. Pour into 9 x 13 pan and bake in 350 F oven for 25-30 minutes or until a toothpick inserted in center comes out clean.  Allow to cool in pan on cooling rack.  Cut into 24 squares for large serving or 48 rectangles for smaller pieces.