Place a piece of parchment paper on an 11×16 baking sheet, or similar

Place the chocolate in a microwave safe bowl and heat in the microwave for 20 second increments, stirring after each time, until fully melted. (you could also heat on the stove top, using the double boiler method)

Spread melted chocolate evenly on parchment paper.

Place in the refrigerator for at least 20 minutes to set up firmly.

Repeat with the white chocolate. Add the peppermint candies to the top while the white chocolate is still melted.

Return the sheet pan to the refrigerator to set fully, about 20-30 more minutes.

Use hands or sharp knife to break into pieces.