Preheat oven to 425°F. In a medium-sized bowl, combine together all the meatball ingredients with clean hands. Form mixture into 1½" meatballs and place on an ungreased baking sheet. Bake in preheated oven for 12-15 minutes or until the meatballs are dark brown and cooked through.
Meanwhile, to prepare the sauce, combine the water, brown sugar, vinegar, worcestershire sauce, ketchup, and grape jam in a small sauce pan over medium high heat. Bring to a boil. Mix the cornstarch with 3 tablespoons of water, and whisk into the sauce mixture. Reduce heat and simmer until the sauce is thick and bubbly, about five minutes.
Toss the meatballs in the sauce and serve immediately, or transfer the sauce and meatballs into a slow cooker on the low or warm setting to keep warm for serving.
Notes
To make these meatballs in the slow cooker: Once the meatballs are cooked through, combine the brown sugar, vinegar, Worcestershire sauce, ketchup, and jelly in the basin of a slow cooker. In a small bowl, whisk together the cornstarch and water, and then whisk the cornstarch slurry into the slow cooker. Add the meatballs, cover, and cook on high for about an hour, until the sauce is thick and bubbly. Reduce heat to warm until ready to serve.