Whisk the gelatin, corn syrup, vanilla, salt and ½ cup boiling water in a stand mixer bowl until the gelatin dissolves.

Using the paddle attachment, beat in the powdered sugar, one cup at at time, on medium low speed, to make a stiff, sticky dough.

Transfer the dough to a clean surface and knead for 5 minutes, adding more confectioner's sugar as needed (up to 1 cup), until the dough is smooth, pliable and slightly tacky.

Divide the dough into 4 pieces. Flatten 1 piece into a disk. Cover the rest with plastic wrap. Add a few drops food coloring and extracts to the flattened disc. 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. Roll out the colored dough on the parchment until ⅛ to ¼ inch thick.

Cut into hearts using 1-inch cookie cutters. Transfer to parchment lined baking sheet. Repeat with remaining dough using different colors and extracts.

Let the cut hearts sit at room temperature, uncovered, until dry and hard, about 24 hours, flipping them about halfway through.

Once dried, write messages on the hearts using food decorating pens.

Store in an air-tight container up to 1 week.