Preheat oven to 350 degrees.
In large bowl with spoon or wire whisk, stir together butter, sugar, and vanilla.
Add eggs, stir until blended.
Stir in flour, cocoa, baking powder, and salt, blend well.
Reserve 2 cups of batter and set aside.
Spread remaining batter into greased and floured 9 x 13 inch pan.
Arrange peppermint patties in a single layer over batter about 1/2 inch apart.
Spread reserved batter over patties.
Bake 50-55 minutes or until brownies begin to pull away from sides of pan.
Cool completely in pan on wire rack before cutting.