In a large pot or Dutch oven, heat the olive oil over medium-high heat and then add the onion and saute for 3 minutes, or until soft. Add the garlic, sauteing for another 1 minute and stirring to prevent burning.
Stir in the ketchup and then fill the ketchup bottle halfway with water (it doesn't have to be exact). Shake it well to release any ketchup sticking to the sides of the bottle. Pour the water into the pot and stir.
Stir in the brown sugar, vinegar, mustard, Worcestershire sauce, molasses, celery salt and pepper. Continue to simmer uncovered over medium-low heat, uncovered so the BBQ sauce can reduce.
Meatballs:
Preheat the oven to 350°F and line a baking sheet with aluminum foil (lightly coated with cooking spray) or parchment paper.
In a large mixing bowl, combine the evaporated milk, bread crumbs, onion, garlic, BBQ sauce, eggs, black pepper and salt. Stir well.
Break the ground beef and pork into small pieces as you add it to the mixture. Toss with clean heads (or wear gloves) until blended. Do not overmix.
Form meatballs into 2-3 inch large meatballs or 1 inch small meatballs and place onto the prepared baking sheet. Bake for 15-20 minutes, depending on size.
Remove and transfer directly to sauce, discarding any grease that came off the meatballs.
Continue to cook uncovered at a low simmer for 60-90 minutes, or until sauce has reduced by a fourth.
Serve over mashed potatoes, rice or couscous.
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