Layer the ingredients. In a 2.5-quart or larger slow cooker, layer the ingredients in this order: peanuts at the bottom, followed by the baking chocolates (60% and 48% cocoa), white chocolate, and candy melts on top. Then, break larger chocolate bars into smaller pieces for even melting.
Cook in the slow cooker. Set the slow cooker to LOW and cover. Let the ingredients cook undisturbed for 1 hour. After the first hour, gently stir the mixture to combine the chocolates and peanuts. Then, continue cooking on LOW for 1½ hours, stirring every 30 minutes, until the chocolate mixture is smooth and glossy.
Cool the mixture. Turn off the slow cooker and keep it covered for 30 minutes. This makes the mixture thicken slightly, making it easier to portion later.
Prepare the baking sheets. Line two large baking sheets with parchment paper or wax paper. This makes sure the candies won’t stick as they cool.
Portion the candies. Using a tablespoon or small cookie scoop, drop 2-tablespoon portions of the mixture onto the prepared baking sheets. Space each candy about ½ inch apart to prevent sticking.
Decorate with sprinkles. While the candies are still wet, sprinkle them generously with red, white, and green holiday sprinkles for a festive touch.
Set the candies. Place the baking sheets in the refrigerator for at least 1 hour or until the candies are completely set and firm to the touch.