2 regular-size peppermint candy canes (one green, one red), crushed
Let egg whites stand at room temperature 30 minutes.
Preheat oven to 225;. Add cream of tartar and salt to egg whites; beat on medium speed until foamy. Gradually add sugar, 1 tablespoon at a time, beating on high after each addition. Continue beating until stiff, glossy peaks form.
Transfer egg whites to piping bag. Pipe 1-1/2-in. cookies 2 in. apart onto parchment-lined baking sheets. Sprinkle half with crushed red candy canes, half with green, or with both.
Bake until firm but not brown, 1-1/2 to 2 hours. Remove to wire racks to cool completely. Store in an airtight container.