Preheat oven to 375?F (190?C). In large bowl, beat softened butter and packed brown sugar with electric mixer until creamy.
Beat in vanilla and eggs. Beat in flour, baking powder, and salt. Drop slightly rounded tablespoons about 2-inches (5 cm) apart onto greased baking sheets.
Flatten cookies slightly and press 5 SMARTIES into top of each. Bake for 8 to 9 minutes.