Put the confectioners' sugar, condensed milk and peppermint extract in a medium bowl and stir together with a fork. Once combined, form a smooth, soft dough with your hands.
Roll out the dough on a surface dusted with confectioners' sugar until it is about 1/8 inch thick. Cut out different shapes with 1 1/2-inch cookie cutters, rerolling the mixture until it is used up. Keep any mixture you are not working with covered with plastic wrap to prevent it from drying out.
Melt the chocolate in a heatproof bowl set over a pan of simmering water or put the chocolate in a bowl and microwave at 30-second intervals, stirring between each one. Dip the peppermint creams into the melted chocolate until they are half covered, then let them cool and set on a baking sheet lined with parchment paper.
If you are storing the creams, pop them in an airtight container spaced apart, dusted with confectioners' sugar and separated between layers of parchment to keep them from sticking together. They can be stored for 2 to 3 days at room temperature.