• Assorted Extracts (such As Peppermint, Strawberry, Or Almond), For Flavoring (optional)
• Cooking Spray
• Food Decorating Pens, For Writing
Whisk gelatin, corn syrup, vanilla, salt, and 1/2 cup boiling water in a stand mixer bowl until gelatin dissolves. Using the paddle attachment, beat in the powdered sugar on medium low speed, 1 cup at a time, to make a stiff, sticky dough.
Note: I would only add up to 4 to 5 cups of powdered sugar into the standing mixer and mix it in. Then turn the dough out onto a powdered sugar covered surface and knead in the rest. The dough gets way too tough for the mixer to stir all the dough. Trust me, when I tried to do this it gave me a scare that I broke my precious mixer.
Transfer the dough to the clean, powdered sugar coated surface and knead, adding more powdered sugar as needed (up to 1 cup) until the dough is smooth, pliable and slightly tacky, about 5 minutes.
Note: After every cup of powdered sugar I kneaded into the rest of the dough, I added 1 tablespoon of water. The end result of the dough should be smooth.
Divide the dough into 4 pieces. Flatten 1 piece into a disk. (Cover the rest with plastic wrap). Add a few drops each of food coloring and extract to the center of the dough; fold in the sides and pinch closed, then knead until the color is distributed.
Lightly coat a large piece of parchment paper with cooking spray lined on a baking sheet. Set aside. Roll out the colored dough on a separate sheet of parchment paper until 1/8 to 1/4 inch thick. Cut into hearts using 1-inch cookie cutters. Transfer to the parchment-lined baking sheet. Repeat with the remaining sections of dough, using different colors and extracts. Let the hearts sit at room temperature, uncovered, until dry and hard, about 24 hours. Write messages on hearts using food decorating pens. Store in an airtight container for up to 1 week.