1. Preheat the oven: Preheat your oven to 200°F (95°C). Line two baking sheets with parchment paper.
2. Prepare the mixing bowl: Ensure your mixing bowl and beaters are completely clean and grease-free. Add the egg whites, cream of tartar, and salt.
3. Beat the egg whites: Using an electric mixer, beat on medium speed until the mixture becomes foamy. Increase the speed to high and beat until soft peaks form.
4. Add the sugar: Gradually add the granulated sugar, one tablespoon at a time, while continuing to beat. Mix until the meringue is thick, glossy, and forms stiff peaks. Rub a little between your fingers; it should feel smooth rather than grainy.
5. Add peppermint flavor: Gently beat in the peppermint extract until evenly combined.
6. Create the swirls: Transfer the meringue to a piping bag fitted with a star tip. For a festive look, paint one or two thin stripes of red gel food coloring inside the piping bag before filling it with the meringue.
7. Pipe the kisses: Pipe small, approximately 1-inch kisses onto the prepared baking sheets, leaving a little space between each one. Sprinkle lightly with crushed peppermint candies if desired.
8. Bake the meringues: Bake for 1 hour 15 minutes to 1 hour 30 minutes, until the kisses feel dry and lift easily from the parchment.
9. Cool slowly: Turn off the oven and leave the meringues inside with the door closed for another hour to dry completely and help prevent cracking.
10. Serve and store: Once completely cool, serve immediately or store in an airtight container in a cool, dry place.