Preheat oven to 180ºC . Melt butter with unsweetened chocolate in the top of a double boiler, stirring occasionally. Set aside to cool. Sift together the cocoa, flour, baking powder and salt. Beat eggs until creamy, then gradually add sugar, beating constantly. Add vanilla and cooled chocolate-butter mixture. Stir in dry ingredients just until combined. Spread batter in buttered 23 cm x 33 cm pan. Sprinkle chips over surface. Bake for 30 to 35 minutes, or until center no longer jiggles when shaken. Cool, then cut into 32 pieces. ---*Dying for Chocolate* Diane Mott Davidson