4 (1 ounce) squares unsweetened chocolate
1 cup butter
1 cup all-purpose flour
1/4 teaspoon salt
4 eggs
2 cups granulated sugar
2 teaspoons vanilla extract
1 1/2 cups chopped pecans

Melt chocolate and butter in a saucepan over low heat; cool.

Stir flour and salt together; set aside.

In a mixing bowl, beat eggs until fluffy. Gradually beat in sugar until thick. Blend in chocolate mixture and vanilla extract. Fold in flour mixture until well blended. Stir in the nuts.

Spread evenly in a greased 13 x 9-inch baking pan. Bake at 350 degrees F for 30 minutes or until firm.

Cool and spread Buttercream Filling over top. Frost with Chocolate Frosting.

Buttercream Filling
1/2 cup butter, softened
2 cups confectioners' sugar
2 tablespoons golden rum
1 teaspoon vanilla extract
Milk or more rum, if needed

Blend all ingredients well until of desired spreading consistency.

Chocolate Frosting
8 (1 ounce) squares semisweet chocolate
1 (3 ounce) white chocolate candy bar
1 to 2 tablespoons solid vegetable shortening

Melt semisweet chocolate in top of double boiler. Cool and spread over  buttercream filling.

Melt white chocolate and 1 tablespoon shortening in top of double boiler. Cook and stir until creamy. Pipe this mixture over top in a checkerboard pattern. Let stand until firm.