Line a large baking sheet with parchment paper or a silicone baking mat. Set aside.

Melt the white chocolate and green candy melts together. Use a double boiler or microwave. If using microwave, stir the chocolate every 20 seconds to help avoid seizing. Once melted and smooth, stir in oil and peppermint extract. Set aside.

Melt the semi-sweet chocolate in the same manner you melted the chocolate in step 2. Pour onto prepared baking sheet and spread out into a large rectangle. Drizzle the white chocolate mixture on top in lines. See photo above for a visual. Use a toothpick or knife to swirl the layers together. Sprinkle the top of the bark with Andes mints, if using.

Allow the chocolate to set at room temperature in a cool, dry environment. My swirled barks usually take around 45 minutes. If needed, you can stick it in the refrigerator to help speed things up. Once hardened, break into pieces as large or as small as you want.