Pre-heat oven to 350ºF - Cover a sheet pan with aluminum foil and set aside until needed
Whisk together all of the ‘glaze’ ingredients in a small bowl - Set aside until needed
Place the three types of meat in a large mixing bowl and, using your hands, loosely combine (does not have to be evenly mixed at this point)
Place half of the mushrooms in the work bowl of a food processor fitted with the chopping blade and pulse into a rough paste - Transfer to the mixing bowl with the meats - Repeat with the other half of the mushrooms - Loosely mix (again, does not have to be evenly mixed at this point)
Cut the onion into 8ths, cut carrots and celery stalks into 1-2 inch pieces and place in the work bowl of the food processor along with the garlic cloves - Pulse into a 'chunky' paste (you want VERY small pieces NOT purée) - Transfer to the mixing bowl with the meats
Add the remaining ingredients, and (again using your hands) thoroughly combine until evenly mixed (DO NOT SQUEEZE THE MIXTURE - Too much 'squeezing', kneading, or 'mashing' will make the final meatloaf 'heavy' and dense)
Place the meatloaf mixture in the center of the lined sheet pan and form into a rectangular 'loaf'
Bake in the top third of the oven for 20 minutes - After 20 minutes, spread half of the glaze (from step 2) evenly over the top and continue to bake for another 20 minutes
Again, after 20 minutes, evenly spread the remaining tomato purée over the top and allow to cook for another 45 minutes or until cooked through (internal temperature should of 160ºF)
Allow to rest for 10 minutes before slicing (DO NOT SKIP THIS STEP!)
Serve hot along with roasted vegetables, smashed potatoes, au gratin potatoes, or baked potato and a salad... really, almost anything!
To 'go the extra mile' and make the dish 'even more':
After meatloaf is baked, heat 2 Tbs of butter in a medium skillet over medium-high heat until shimmering
Fry 1-2 slices of meatloaf per person until browned and crusted (apx 1 minute per side) - Fry 1 serving at a time and wipe out skillet and replace butter every batch to ensure butter doesn't burn
Serve hot (perfect for dinner but absolutely wonderful with scrambled eggs for breakfast!)