In a large mixing bowl, combine the sweetened condensed milk and peppermint extract. Stir until evenly blended.
Using an electric mixer, gradually add the 4 cups powdered sugar, mixing until a firm, smooth dough forms. The dough should be stiff enough to hold its shape without feeling sticky.
Line a baking sheet or tray with parchment paper and set aside.
Divide the peppermint mixture into 24 portions and roll each portion into a ball.
Place the dough balls onto the prepared tray, then gently flatten each one into a thick, round disc measuring approximately 2 inches in diameter and ¼ inch thick.
Transfer the tray to the freezer and chill the peppermint patties for about 1 hour, or until completely firm.
Place the chocolate almond bark in a microwave-safe bowl. Microwave in 30-second intervals, stirring after each interval, until the chocolate is completely melted and smooth.
Remove the chilled peppermint patties from the freezer. Working quickly, dip each patty into the melted chocolate, making sure it is completely coated on all sides.
Gently shake off any excess chocolate or carefully scrape the bottom of each patty against the edge of the bowl.
Place the chocolate-covered patties back onto the parchment-lined tray.
If desired, immediately decorate each patty with sprinkles while the chocolate coating is still soft.
Allow the chocolate coating to set completely before serving.