Preheat oven to 350 degrees.
In a mixing bowl cream butter and sugar.
Add eggs and vanilla, mix well.
Combine flour, cocoa, baking powder, and salt. Stir into creamed mixture just until blended.
Pour into 2 greased 9 inch square pans.
Sprinkle with chips and nuts.
Bake for 35-40 minutes or until a toothpick inserted in center comes out clean.
Cool completely before cutting.