Preheat oven to 350 degrees F (180 degrees C). Grease an 8 inch square baking pan.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs, one at a time. Add the vanilla, cocoa powder, baking powder, flour and salt. Mix until just combined.
Spread the batter evenly in the prepared pan. Sprinkle the chocolate chips and nuts (if using) over the top. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Allow to cool completely before serving.
Interesting Facts
Chocolate Surprise is also known as Death by Chocolate.
The original recipe called for a layer of frosting or ganache on top, which can be added if desired.