Grease 9-inch square pan well; line with foil. Preheat oven 350 F degrees. Resift flour with baking powder and the salt. Melt butter with chocolate over low heat. Beat eggs with sugar until light. Add flour mixture, chocolate mixture, and 1/4 cup Kahlua; blend well. Stir in nuts.
Turn into prepared pan. Bake 30 minutes, or until top springs back when touched lightly in the center, and edges begin to pull away from the pan. Remove from oven; cool thoroughly in pan. Brush top with 1 tablespoon Kahlua. Cut into 1 x 2-inch bars. Garnish, if desired