Preheat oven to 350 degrees F

Coat square 8x8 inch pan with non-stick cooking spray

In a large bowl, cream together butter and sugar

Add vanilla extract and eggs. Stir until smooth and creamy.

Stir in flour, cocoa powder, baking powder and salt until well combined

Stir in chocolate chips or chopped walnuts, if using

Spread evenly into prepared baking pan

Bake at 350 degrees F for 25 minutes or until a toothpick inserted comes out clean

Cut into squares

Store in airtight container