Line an 8x8-inch square baking pan with foil or parchment paper. Set aside.
Place the chocolate into a large microwave-safe bowl, and heat in 20 second intervals, stirring after each one, until melted and smooth. Stir in the peppermint extract and food colouring.
Stir in the condensed milk and chopped Oreos. The mixture will become thick.
Spread the mixture into the prepared pan, and smooth out the top. Sprinkle with extra chopped Oreos, if desired. Refrigerate for 2 - 4 hours or overnight until completely set.
Notes
Fudge can be stored in an airtight container at room temperature for 1 week, or in the fridge for 2 - 3 weeks. It also freezes well for up to 2 months. Thaw overnight in the fridge before serving.