In a large bowl, mix together milk, egg, garlic, and seasonings. Fold in ground beef, rolled oats, cracker crumbs and onion. Mix just until combined. Form into meatballs and place in a baking dish.
Sauce
In a small saucepan, bring half-and-half to a simmer. Add cream cheese and whisk until smooth. Add Dijon, cheese, and seasonings. Stir until cheese is melted. Spoon on top of meatballs.
Bake for 45 minutes uncovered, or until internal temperature reaches 160 F. Garnish with parsley and serve.