Line 2 - 3 large baking trays with parchment or wax paper, and set aside.

In a large bowl, mix together the condensed milk and peppermint extract. Mix in the icing sugar until a thick dough forms.

Roll the dough into 0.5oz balls (lightly coat your hands in icing sugar if needed), and place them onto the prepared baking trays. Press each ball into 1/4-inch thick circles. Freeze for 30 minutes.

Line a muffin pan with muffin cases, and set aside.

Add the chocolate and oil to a large microwave-safe bowl, and heat in 30 second intervals, stirring after each one, until melted and smooth.

Add 1 teaspoon of melted chocolate into each muffin case, place a patty in the middle, then top with 1 - 2 teaspoons of more chocolate. Tap the tray on the surface serveral times to level out the chocolate.

Refrigerate or freeze until the chocolate has set.

Repeat with the rest of the patties. Return the melted chocolate to the microwave for 20 - 30 seconds if it cools too much, and begins to set.