01 - Line a baking sheet with parchment paper or a silicone mat.
02 - Melt the semisweet chocolate in a heatproof bowl over a pan of simmering water (or microwave in 30-second bursts, stirring each time) until smooth. Stir in ½ tsp peppermint extract.
03 - Pour the melted semisweet chocolate onto the prepared baking sheet and spread into a rectangle about 9x12 inches.
04 - Melt the white chocolate using the same method. Stir in the remaining ½ tsp peppermint extract.
05 - Drop spoonfuls of the melted white chocolate over the semisweet base. Use a skewer or knife to swirl the two chocolates together for a marbled effect.
06 - Immediately sprinkle the green M&Ms or mint candies, green sprinkles, and mini chocolate chips evenly across the surface.
07 - Gently press the toppings into the chocolate.
08 - Refrigerate for at least 30 minutes until fully set.
09 - Break or cut into pieces and serve.