Line a 7-inch x 11-inch baking dish with parchment paper. Set aside.
To a heavy-bottom medium saucepan, add the sweetened condensed milk, chocolate chips, and peppermint extract. Place over medium-low heat. (Do not use high heat or you may burn your fudge!)
Heat the fudge ingredients, stirring often until the chocolate is fully melted and everything is evenly incorporated, about 5-8 minutes.*If you notice the chocolate is heating too much and getting thick and crumbly, turn the heat down.
Remove from the heat and pour the mixture into the prepared baking dish. Sprinkle crushed peppermints over the top of the fudge for garnish if desired.
Let the fudge set up on the counter for at least 1 hour. You can speed this process by putting it in the fridge.
Cut into 1-inch squares (4x7 grid) and enjoy!
Notes
You'll need to purchase two 12-ounce bags of chocolate chips to have enough. There will be about ½ cup extra once you've used what you need for the recipe.