3 cups semisweet chocolate chips (such as Hershey's® Special Dark)
1 (14 ounce) can sweetened condensed milk
1/4 cup butter
1 1/2 teaspoons pure peppermint extract
1 pinch salt
1/2 cup crushed peppermint candies, or more to taste
Combine chocolate chips, sweetened condensed milk, butter, peppermint extract, and salt in a large microwave-safe bowl.
Heat in the microwave on medium-high until chips are melted, 5 to 6 minutes, stirring every 2 minutes.
Pour chocolate mixture into an 8x8-inch silicone baking dish; top with crushed peppermint candies. Lightly press candies, using the back of a spoon, into chocolate mixture. Refrigerate until set, 1 hour.