From: Jenn@eatcakefordinner
3/4 c. unsalted butter, room temperature
2 c. packed light brown sugar
3 large eggs
2 tsp. vanilla extract
3 1/2 c. all-purpose flour
1 Tbl. baking powder
1/2 tsp. salt
1 (18.4 oz.) bag Peanut Butter M&M's
Preheat oven to 350 degrees. Cream together the butter and brown sugar. Add the eggs, one at a time, beating after each addition. Add the vanilla and mix until combined. Add the flour, baking powder and salt and mix until just combined. Stir in the Peanut Butter M&M's. Press dough into a greased 9x13-inch cake pan. Bake for 20 minutes. Cool, cut into bars and serve.