Preheat oven to 350°F. Prepare 24 cavity bite-sized heart dessert shell pans with a cake release spray coating.
In large bowl, combine flour, cocoa, baking powder, baking soda and salt.
In large bowl, beat butter and sugar with electric mixer until light and fluffy. Add egg and vanilla extract; beat until well combined. Alternately add flour mixture and buttermilk in three additions, beating until just combined. Spoon one tablespoon batter into each pan cavity.
Bake 9-11 minutes or until tops of cakes spring back when touched. Cool in pan 10 minutes. Cool completely on cooling grid.
To decorate, place cakes on cooling grid with cookie pan below. Pipe 1/2 teaspoon peanut butter, chocolate fudge or cherry pie filling into shell; fill only to top of cavity. If desired, warm glaze according to package instructions; carefully pour and tap pan to smooth.