Heat oven to 350 degrees F. Heat butter and chocolate in a small sauce pan on low heat, stirring constantly until melted.

Using an electric hand mixer, mix the sugar, vanilla, and eggs on high in a large mixing bowl. Stir in chocolate mixture. Add the dry ingredients and mix until blended.

Spread the mixture into a greased 8x11x2 baking dish. Bake until a knife inserted in the center comes out clean. 25 to 30 minutes