Preheat oven to 350F. (non-convection/not fan-assisted) Cover a rimmed baking sheet with heavy-duty aluminum foil (or two layers of regular aluminum foil). Set aside.
Make the tomato sauce: In a medium bowl, stir together all the tomato sauce ingredients until smooth. Set aside.
Make the meatloaf mixture: 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 about 1/3 of the prepared tomato sauce to the beef mixture and stir in 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 (using damp hands is sometimes helpful), shape into a loaf shape about 3 inches high x 4 inches wide x 9 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 of the meatloaf and, using the back of a spoon, spread it over the top, trying to keep most of it on top. Spread a bit along the sides, as well.
Bake the meatloaf in a preheated oven for about 1 hour, or until the meat registers 160F when tested with an instant-read thermometer. Allow the meatloaf to rest 3 or 4 minutes before slicing.
Serve garnished with parsley or Parmesan, if desired. Great served with mashed potatoes and a green vegetable.
Notes
Note 1: I have always preferred this meatloaf with tomato paste, but it is also very good made with tomato sauce. If using canned tomato sauce, start with a 13 oz/398 ml can and use the whole can. You could also use half tomato paste and half tomato sauce (and freeze the remainder of each can for a future meatloaf). Try them all the ways and pick your family's favourite.Note 2: One thing to note is that the salt on the crackers will add a bit of saltiness to the meatloaf, and there is also salt in the tomato sauce. The amount will vary by brand, so it's hard to judge exactly how much extra salt you need to add to the meat. I've settled on 1 tsp, which should be close. If you find that the finished meatloaf is a touch under-salted, you can always salt the finished meatloaf a bit. Easier to add than take away :)Note 3: If you don't have soda crackers, you can use other types of crackers (that aren't heavily flavoured) or add a couple of tablespoons of dried bread crumbs or even a slice of bread crumbled up.For a gluten-free version, substitute gluten-free rolled oats for the crackers. Simply process them lightly to break them up a bit and use them in the same 1/4 cup quantity as for the crushed crackers.Be sure to read the notes about the Recipe Card, where you'll find Step-by-Step photos and a Recipe Video that you might find helpful.