Step 1: In a large bowl, using an electric mixer, cream together the softened unsalted butter and shortening until light and fluffy. Scrape down the sides of the bowl.
Step 2: Gradually add the sifted confectioners' sugar, alternating with the heavy cream, mixing on low speed until combined. Increase speed to medium and beat until smooth and creamy.
Step 3: Stir in the pure peppermint extract and optional green food coloring until fully incorporated and the desired color is achieved.
Step 4: Cover the bowl with plastic wrap and chill the peppermint mixture in the refrigerator for at least 30 minutes, or until it is firm enough to handle easily.
Step 5: Line a baking sheet with parchment paper or a silicone mat. Lightly dust your hands with confectioners' sugar. Take about 1 tablespoon of the chilled peppermint mixture and roll it into a ball, then flatten it into a disc approximately 1/4 inch thick and 1.5 to 2 inches in diameter. Place the shaped patties on the prepared baking sheet.
Step 6: Once all the patties are shaped, place the baking sheet in the freezer for 20-30 minutes, or until the patties are very firm. This helps them hold their shape and prevents melting when dipped in warm chocolate.
Step 7: While the patties are freezing, melt the chocolate. In a microwave-safe bowl, combine the chopped dark chocolate and coconut oil (or additional shortening). Microwave in 30-second intervals, stirring well after each, until the chocolate is smooth and completely melted. Alternatively, melt over a double boiler.
Step 8: Remove a few frozen patties from the freezer at a time. Drop one patty into the melted chocolate, fully coating it. Use a fork or a dipping tool to lift the patty out, allowing any excess chocolate to drip back into the bowl. Lightly scrape the bottom of the fork against the edge of the bowl.
Step 9: Carefully place the chocolate-coated patty back onto the parchment-lined baking sheet. Repeat this process with the remaining patties, working quickly so the patties remain cold. If the chocolate starts to thicken, gently rewarm it.
Step 10: If desired, immediately after dipping, sprinkle with flaky sea salt or crushed candy canes, or drizzle with contrasting melted white chocolate. Place the finished patties in the refrigerator for at least 15-30 minutes to allow the chocolate to fully set and harden.
Step 11: Once set, transfer the homemade peppermint patties to an airtight container. Store them in the refrigerator for up to 2-3 weeks, or freeze for longer storage. Enjoy your delightful homemade treats!