Prep the pan: Line an 8-inch square pan with parchment, leaving overhang for easy lifting. Lightly grease the parchment.
Melt the chocolate: Add chocolate chips and sweetened condensed milk to a medium saucepan. Warm over low heat, stirring constantly, until smooth and glossy.
Don’t let it simmer.
Add peppermint: Remove from heat. Stir in 1 teaspoon peppermint extract. Taste a tiny bit (careful, it’s warm).
Add up to ½ teaspoon more if you want a stronger mint flavor.
Spread and level: Scrape the mixture into the prepared pan. Smooth the top with an offset spatula or the back of a spoon.
Top it off (optional): Sprinkle crushed candy canes or a pinch of flaky sea salt. Press lightly so toppings adhere.
Chill: Refrigerate until firm, about 2–3 hours.
For the cleanest cuts, chill at least 4 hours or overnight.
Slice and serve: Lift the fudge out by the parchment. Use a warm, sharp knife (run under hot water, wipe dry) to cut into 1-inch squares.