Use a non-toxic marker or a pencil to draw a little dot on the outside of 12 cupcake liners, then place them in your cupcake pan. Set aside.
Mix up your vanilla cake batter according to the recipe’s instructions.
Pour a little more than 1/3 of the batter (about a cup and a half) into a smaller bowl.
Add red food coloring until you get your desired pink or red color.
Pour the batter into a non-stick (or lightly greased) 8x8 baking pan and bake until the edges of the cake start to turn golden brown and a toothpick inserted into the center of the cake comes out clean (different recipes will require different baking times—be sure to keep an eye on your cake).
Allow to cool completely (to speed up the process, stick it in the fridge).
Once the sheet cake is cool, loosen the edges away from the pan with a knife and then invert the pan onto a cutting board.
Use a small heart-shaped cookie cutter to cut out a dozen cake hearts that are small enough to fit into an average-sized cupcake pan.
Spoon two heaping tablespoons of the remaining batter into paper-lined cupcake tins, so they’re about half-full. Put one heart into each tin and press it point down into the batter. (Keep all the hearts facing towards the dot you drew on the cupcake paper, so you remember which way the heart is facing after the cupcakes are baked.) Cover with another heaping teaspoon of batter so the heart is completely covered and bake until the cupcakes have turned golden brown and the cake bounces back when you gently press your finger into the top of the cupcake.