In a double boiler over low heat, combine 2 cups of dark or semi-sweet chocolate chips, 1 tablespoon of butter, and 1 can of room temperature sweetened condensed milk. Stir continuously until melted and smooth, about 5-7 minutes.

In a separate bowl, melt 1½ cups of white chocolate chips together with ⅓ cup of sweetened condensed milk using gentle heat, stirring until silky and melted, about 3-5 minutes. Add gel food coloring and mix until vibrant.

Grease an 8x8-inch square pan. Pour about ¾ of the chocolate mixture into the pan, spreading evenly. Dollop spoonfuls of white chocolate on top and swirl gently using a skewer or toothpick.

Spoon remaining chocolate into gaps of white chocolate, swirl gently again, then sprinkle crushed peppermint candy on top.

Chill in the refrigerator uncovered for at least 3 hours until firm.

Remove from pan and cut into squares using a hot knife for clean edges.