The secret to perfect hearts (or whatever shape you choose) is cookies! Start by baking a batch of basic sugar cookies. To save time, we began with a Betty Crocker Cookie Mix and added 1/3 cup butter, 1 tablespoon flour and an egg. On a floured surface, roll the dough to about 1/4-inch thickness. For each cupcake you’ll need four cookies—three to be baked inside and one to be placed on top for decoration. We found that cutters that are 1- to 1 ¼-inch work best. Arrange cookies on ungreased sheets 1 inch apart and pop into a 375°F oven for 7 to 9 minutes or until edges are light golden brown. Cool for 1 minute; remove from cookie sheets and allow to cool completely for 15 minutes.
Next, reduce the oven temperature to 350°F and make the cake batter according to package directions. Place paper liners in 24 regular-size muffin cups. Spoon a heaping tablespoon of the cake batter into the bottom of each liner.
Place a row of three cookie hearts in middle of each liner so that they are standing up in the batter. Mark the paper liner to identify the front of the cupcake. (We like to make a small cut in the paper liner to mark the front.)
Spoon two heaping tablespoons of the remaining cake batter on top of the cookie hearts being careful to not tip them over.
The cookies will stick out from the batter, but the cupcake will bake up around them. Covering them completely with batter will cause the cupcakes to overflow while baking.
Bake cupcakes 22 to 27 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes in pan then remove to cooling rack and allow to cool completely. Note: Tops may appear sunken; that’s normal and frosting will serve to disguise those dips.
To make the frosting, beat marshmallow creme, 1 cup butter and 1 tablespoon of the milk with electric mixer on medium speed until blended. Beat in powdered sugar. Add more milk, 1 teaspoon at a time, as needed until fluffy and spreadable.
Decorate each cupcake by either piping or spreading frosting with an offset spatula (a butter knife works as well too). Then, use the mark you made on the paper liners to find the front of the cupcakes. Place the remaining cookie hearts on top with the cookies facing the front so people will know which direction to cut (or bite) into the cupcake to see the heart inside.