In a saucepan over medium heat, combine the cranberry jelly, chili sauce, Dijon mustard, brown sugar, and fresh lemon juice. Stir the mixture frequently, allowing it to simmer for 5 to 10 minutes until the cranberry jelly softens and the sauce is well blended. This will create a flavorful, tangy-sweet sauce that coats the meatballs perfectly. I like to taste the sauce at this point and adjust the sweetness or acidity if needed.

Place the fully cooked meatballs (fresh or frozen) in a 6-quart slow cooker. Pour the hot cranberry-chili sauce (from Step 1) over the meatballs, then gently mix to ensure all meatballs are evenly coated in the sauce.

Set the slow cooker to LOW, cover, and cook for 2 hours if using fresh meatballs, or 3 hours if the meatballs are frozen. Once the meatballs are heated through and the sauce is bubbling, switch the slow cooker to the WARM setting to keep the dish hot until ready to serve. This step ensures the flavors meld and the meatballs stay juicy.

Transfer the warm meatballs to a serving dish or serve them directly from the slow cooker, making sure each serving is generously coated with the tangy cranberry-chili sauce. Garnish with fresh herbs, like parsley, if desired. For parties, I like to offer toothpicks for easy snacking.