Preheat oven to 350°F. Unwrap candies and remove papers.
Beat brown sugar, butter, eggs, corn syrup and vanilla in large mixer bowl until well blended. Gradually beat in flour, cocoa powder, salt and baking powder.
Drop by heaping tablespoonfuls into a greased mini muffin tin. Bake for 12 to 14 minutes until cookies are set but still soft. Press a peanut butter cup into each cookie.
Cool completely and remove from pans.