Preheat oven to 350. Grease 8x11 pan.
Break the semisweet and unsweetened chocolate into 1-ounce pieces.
Bring the butter to a boil in a medium size saucepan. Add both chocolates and immediately remove from heat. Stir until the chocolate melts completely.
Combine the flour, baking powder and salt in a small bowl, set aside.
Combine the eggs and sugar in the bowl of an electric mixer. Beat until the mixture is very thick and forms ribbons when you lift the beaters away from the batter.
Add the vanilla and blend lightly. Add the melted chocolate and mix lightly.
Gently fold the flour mixture into the chocolate batter with a spatula. Fold in the chocolate chips and nuts..Spread batter in greased pan.
Bake for 35 to 40 minute, when done, a cake tester in the center will have a little batter clinging to it.. Do not over bake. Cool in pan.