Preheat oven to 375.

Heat butter in a skillet over medium-low heat. Butter will start to foam while cooking. Continue cooking until little brown bits start to form at the bottom and the butter has a nutty aroma. Remove from heat. Allow to cool.

Combine muffin mix, vanilla, egg and browned butter in a bowl. Mix well.

Press mixture into an ungreased 15 x 10 inch jelly roll pan. Bake in preheated oven for 15 - 20 minutes or until browned. Remove from oven.

Melt semi-sweet chocolate chips in the microwave at 30 second intervals until melted. Use a fork to drizzle chocolate over the top of cookie brittle.

Melt white chocolate chips in the microwave at 30 second intervals until melted. Use a fork to drizzle white chocolate over the top of cookie brittle.

Sprinkle with sprinkles if desired. Break cookie bark into irregular pieces. Serve.