1/4cupcider or white vinegar, I generally use white, but try both and see which one you prefer
1tspprepared yellow mustard
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Preheat oven to 350F. Cover a baking sheet with heavy-duty aluminum foil (or two layers of regular aluminum foil). Set aside.
In a medium bowl, make the sauce by stirring together the sauce ingredients until smooth. Set aside.
In a large bowl, add the ground beef, egg, salt, pepper, crushed crackers and diced onion. Using a large spoon, stir to combine well. Add a little less than 1/2 of the prepared sauce to the beef mixture. Stir to combine well.
Drop big spoonfuls of the ground beef mixture into a rough log shape in the centre of the prepared baking pan. Using your hands, shape into a loaf shape about 2-3 inches high x 3 inches wide x 10-12 inches long. Try to keep the top of the loaf flat, so the sauce will stay on the top as it cooks. Spoon the remaining sauce over the top, along the length of the meatloaf. Use a spoon to spread over the top, trying to keep most of it on top. Spread a bit along the sides.
Bake in preheated oven for 1 hour, or until the meat registers 160F when tested with an instant read thermometer. Allow to rest several minutes before cutting. Serve garnished with parsley or Parmesan, if desired. Great served with mashed potatoes and a green vegetable.
Be sure to read the Ingredient and Cook's Notes above the Recipe Card, where I share more detailedtips, variations and substitution suggestions for this recipe! You'll also find Step-by-Step photos there, if you'd like to see my meatloaf being made.