Melt both chocolates and butter in double boiler over medium heat until smooth.

In a separate bowl, mix eggs, both sugars, and vanilla extract. Add melted chocolate, flour, baking powder, and salt. Remove two and one-fourth cups of mixture and set aside.

Add two-thirds of nuts to original mixture and mix well. Spread in a nine- by 13-inch pan or two eight-inch round pans.

Beat cream cheese and butter until smooth. Beat in vanilla extract and sugar; add eggs, one at a time.

Pour cheese mixture over chocolate mixture and spread to edges of pan.

Stir reserved chocolate mixture well and pour large spoonfuls over cheese layer.

Spread with knife blade in a zigzag pattern to marbleize. Sprinkle with remaining nuts.

Bake at 350 degrees Fahrenheit for one hour and 15 minutes.