In a mixing bowl, combine the powdered sugar, light corn syrup, water, peppermint extract, and softened butter. Mix until a dough forms. If it’s too sticky, add a little more powdered sugar until it’s a thick, smooth dough.
Place the dough between two sheets of parchment paper. Use a rolling pin to roll the dough out to about 1/4-inch thickness. Place everything (with parchment paper) on a large baking sheet and freeze for 15-20 minutes to make the cutting process easier.
Remove from the freezer, peel the top piece of parchment paper. Use a small round cookie cutter (about 1 to 1.5 inches in diameter) to cut out the mint patties. Carefully transfer the cutouts to a different parchment-lined baking sheet. Place in the freezer for 5 or so minutes while you prepare your chocolate.
While the patties are freezing, melt your chocolate. You can do this in the microwave in 30-second increments, stirring between each, or using a double boiler. Stir in the coconut oil for a smoother coating, if using.
Pull the patties out of the freezer then dip each one into the melted chocolate using a fork to coat both sides. Let the excess chocolate drip off, then place them back onto the parchment paper.
Let the chocolate-covered patties sit at room temperature or place them in the fridge for about 10-15 minutes to set.
Once the chocolate has hardened, your homemade York Peppermint Patties are ready to enjoy! Store them in an airtight container at room temperature or in the fridge.