Line a baking sheet with parchment paper and set aside.
Melt the dark chocolate chips in a microwave-safe bowl in 30-second intervals, stirring between each, until completely smooth.
Stir in the peppermint extract, then pour the chocolate onto the prepared baking sheet and spread into an even layer about 1/4-inch thick.
Melt the white chocolate chips using the same method, then drizzle over the dark chocolate layer.
Use a toothpick or knife to swirl the white chocolate into the dark chocolate, creating a marbled effect.
Immediately sprinkle with crushed peppermint candies and almonds if using.
Refrigerate for at least 1 hour until completely set, then break into pieces and store in an airtight container in the fridge.