01 - Line a baking sheet with parchment paper and lightly dust with powdered sugar.
02 - In a medium heavy-bottomed saucepan, mix granulated sugar, water, corn syrup, and cream of tartar. Stir over medium heat until sugar dissolves.
03 - Stop stirring and bring mixture to a boil. Use a candy thermometer to cook until temperature reaches 260°F (127°C).
04 - Remove from heat and wait for bubbles to subside. Stir in peppermint extract.
05 - Divide syrup into two heat-proof bowls if using color. Add red gel food coloring to one bowl; leave the other clear.
06 - Working quickly, pour alternating stripes of each color onto prepared sheet. Use an oiled knife or bench scraper to shape into a log or rope.
07 - When slightly cool but pliable, twist ropes together for a peppermint swirl. Cut into 1/2-inch pieces with greased scissors or a sharp knife.
08 - Allow candies to cool and harden at room temperature. Dust with powdered sugar to prevent sticking. Store in an airtight container.