How to Make It
Line 2 baking sheets with parchment paper. Stir together condensed milk, powdered sugar, and peppermint extract in a large bowl using a wooden spoon until combined. (Mixture will be very thick.)
Transfer peppermint mixture to a work surface heavily dusted with powdered sugar. Knead until a smooth ball forms, kneading in more powdered sugar as needed to form a very firm dough. Roll out dough to 1/3-inch thickness. Cut out rounds using a 1 1/2-inch round cookie cutter, and arrange on prepared baking sheets spaced 1 inch apart. Reroll scraps once. (You will have about 48 rounds total.) Chill 30 minutes.
Microwave chopped chocolate and coconut oil in a microwavable bowl on HIGH until fully melted and smooth, about 2 minutes, stopping to stir every 30 seconds.
Remove peppermint rounds from refrigerator. Using a fork, dip each round in melted chocolate mixture, coating both sides completely and letting excess drip back into bowl. Return dipped patty to parchment-lined baking sheet; decorate with crushed peppermints. Repeat process using remaining rounds.
Chill dipped patties until set, about 30 minutes. Store in an airtight container in refrigerator up to 5 days.