Pre-heat oven to 300°F.
Separate the eggs from the egg whites (if using fresh eggs). Measure out 100 g (about 3 large eggs).
Dry Ingredients: In a separate bowl, sift the icing sugar, and almond flour together. Repeat the sifting process to ensure there are no clumps. If there are any clumps, discard them.
Prepare the Meringue: In a stand mixer fitted with the whisk attachment (or bowl if using a hand mixer), add the egg whites and a pinch cream of tartar. Beat on high until foamy.
Once the egg whites are foamy, turn the mixer down to the lowest setting possible, and slowly add in the granulated sugar. Be sure to incorporate all the sugar into the egg whites.
Turn up the mixer again on high, and keep beating egg whites until stiff peaks form. DO NOT OVER BEAT.
Macronage: With a rubber spatula, fold the dry mixture into the egg whites, just until combined.
Divide the batter into 4 separate bowls.
Using a toothpick or scribe, add a smidge of preferred gel food color, then macronage as usual, until the paste flows like a ribbon/lava.
Repeat with the other 3 colors.
Prepare a baking sheet with a heart template, then lay on top of it parchment paper or silicone baking mat.
Fit a pastry bag with a #12 round tip, if using, and trim the bottom as appropriate. Transfer one color to the piping bag.
Pipe hearts onto the prepared baking sheet. Once the frist color is piping, tap the baking sheet to release all air bubbles. Remove smaller bubbles with a cookie scribe or toothpick.
Repeat this process with each color. You should get about 80 mini hearts in total if following the template.
Rest for 30 minutes, until the shells have formed a skin, and are no longer tacky to touch.
Bake Shells: Bake in the oven, at 300ºF-325°F for 8-10 minutes.
Check for doneness, by wiggling the shell. Shells are done when they don’t move from the feet. If it wiggles from the feet, then bake for another minute, and check again.
Cool the shells in the tray.