Beat eggs until thick and lemon colored in a small mixing bowl. Add next 4 ingredients; mix well. Set aside.
Combine 1/2 cup butter, egg yolk, and water; beat until light and fluffy. Add flour, baking powder, and 1 teaspoon sugar; mix well. Press mixture into a lightly greased 13- x 9- x 2-inch baking pan. Bake at 350° for 10 minutes.
Sprinkle chocolate morsels over crust. Return to oven for 1 minute. Remove from oven, and spread melted chocolate evenly over crust using a spatula.
Pour reserved egg mixture over chocolate, spreading evenly. Return to oven, and bake an additional 35 minutes. Cool and cut into 1 1/2-inch squares.