Heat oven to 350 degrees. Grease 13"x9"x2" baking pan. In large bowl with spoon or wire whisk, stir together butter, sugar and vanilla. Add eggs, stir until well mixed. Stir in flour, cocoa, baking powder and salt; blend well. Reserve 2 cups batter; set aside. Spread remaining batter in prepared pan. Arrange peppermint patties in single layer over batter about 1/2" apart. Spread reserved 2 cups batter over patties. Bake 50 to 55 minutes or until brownies begin to pull away from edges of pan. Cool completely in pan. Cut into squares. About 36 brownies.