Preheat the oven to 190ºF.

Combine the egg whites, sugar, and cream of tartar in a double boiler set over simmer water (or in a medium heatproof bowl set over a pot of simmering water, making sure that the bottom of the bowl does not touch the water). Whisk mixture continuously until the sugar has dissolved and the egg whites are warm to the touch, about 3-5 minutes.

Strain the mixture through a fine metal sieve into the bowl of a stand mixer fitted with a whisk attachment.

Whisk on low-speed, gradually increasing to high-speed until soft peaks form (about 5 minutes). Add vanilla extract (or extract of choice) and, if using, food dye, and continue beating on high-speed until stiff peaks form (about 2 minutes).

Transfer the meringue to a pastry bag fitted with a wide tip (or, as I do, a Ziploc bag with a hole cut in the bottom corner for a pastry tip)

Pipe 2-inch hearts onto a parchment-lined baking sheet. **Note: I then used a toothpick to adjust the shape of the hearts

Bake until crispy on the outside and soft on the inside, about 1¼ to 1½ hours (Taste one after 1¼ hours to check whether they're done), and remember: do not open the oven door during the first hour the meringues are baking). After the meringues are done baking, turn the oven off and open the door to let meringues cool slowly in the oven (or eat right away because they're so super yummy you just can't wait!).