Pile these pretty heart shaped cookies on a plate and let guests fill them with assorted jams and preserves.
Preheat oven to 375 degree F. In a large bowl beat butter with an electric mixer on medium to high speed for 30 seconds. Add granulated sugar, brown sugar, baking powder, and salt. Beat until mixture is combined, scraping sides of bowl occasionally. Beat in egg, milk, and vanilla until combined. Beat in as much of the flour as you can with the mixer. Stir in any remaining flour.
Shape dough into 3/4-inch balls. For each cookie on an ungreased or parchment paper-lined cookie sheet place 2 dough balls side by side with one side touching. Press thumbs into each ball to form an indentation in each. Press in center of each with thumb and taper bottom of cookie with fingers to form a heart shape. Repeat with remaining dough balls, leaving about 2 inches between cookies.
Bake for 7 to 9 minutes or until edges are lightly browned. Remove from oven and transfer cookies to a wire rack. While warm, fill each indentation with jam or preserves (if necessary, snip any large pieces of fruit). Cool completely. Makes about 30 cookies.
Place filled cookies in a single layer in covered storage containers and store at room temperature up to 3 days or freeze up to 3 months.