Preheat oven to 225°F and line two baking sheets with parchment paper.
In a completely clean, grease-free bowl, beat egg whites and cream of tartar on medium speed until soft peaks form.
Gradually add sugar one tablespoon at a time while beating on high speed until stiff, glossy peaks form, about 8-10 minutes.
Gently fold in peppermint extract and salt until just combined.
Drop rounded tablespoons of meringue onto prepared baking sheets, spacing them 1 inch apart.
Bake for 90 minutes, then turn off oven and let meringues cool completely inside with door cracked open for at least 2 hours.
Melt dark chocolate in a microwave-safe bowl in 30-second intervals, stirring between each, until smooth.
Dip the bottom half of each cooled meringue into melted chocolate, allow excess to drip off, then sprinkle with crushed peppermint.
Place on parchment paper and let chocolate set completely before serving.