Combine butter and cream cheese in a large mixing bowl, beating until light and fluffy. Add flour, 2 tablespoons sugar, and baking powder, stirring until well blended.
Roll dough to 1/4-inch thickness on a lightly floured surface. Cut with a 1 1/2-inch fluted or round cutter. Place 2 inches apart on ungreased cookie sheets. Press center of each cookie slightly with thumb. Fill center of each cookie with 1/4 teaspoon jam.
Bake at 350° for 10 to 12 minutes. Remove from cookie sheets, and place on wire racks to cool. Sift powdered sugar over tops of cookies, if desired.