Make glaze by whisking all glaze ingredients in a saucepan until sugar dissolves. Reserve 1/3 cup glaze mixture, then simmer remaining glaze over med-low heat until slightly thickened, about 5 minutes. Cover and keep warm.
Heat oil in a skillet over med heat; cook onion until soft and starting to brown at the edges. Add garlic and cook one more minute. Remove from heat and set aside to cool.
In a large bowl, mix the beef, pork, and turkey by hand until combined. Process the saltines in a food processor into a fine texture, or place in a zip-type bag and crush with a rolling pin.
Add the crackers to the milk in a small mixing bowl. Add the eggs and yolk, mustard, Worcestershire sauce, thyme, parsley, salt and pepper, along with the cooked onions and garlic to the milk and cracker paste; mix well and then add to the meat until well incorporated.
Divide and shape mixture into two loaves, side by side, on a parchment-lined, rimmed baking sheet. Trim parchment paper around outside edge of loaves to remove excess, leaving about an inch around loaves.
Shape meat mixture into two loaves, side by side, on a parchment-lined, rimmed baking sheet. Trim parchment paper to remove excess, leaving about an inch around loaves. Broil on HI, 5-6 inches away from element, until browned, 8-10 minutes. Brush the reserved, uncooked glaze over top and sides of the loaves.
Move the oven rack to the middle position and bake loaves at 350°F for 30-35 minutes or until the center of the loaves reach 160°F. Transfer to carving board, tent with foil, and let rest 10 minutes.
Serve with cooked glaze at the table.
Total Time includes resting time.To make this gluten-free, use GF crackers or GF bread crumbs. If using bread crumbs, increase salt by 1/4 teaspoon.For make-ahead meals: Make into smaller loaves (adjust baking time), cool and freeze loaves without sauce. Sauce can be prepared and frozen separately. Slice defrosted meatloaf and gently reheat individual portions in a skillet and top with warmed sauce.Cooking the loaves on parchment isn't absolutely necessary, but it makes clean-up a breeze and I like that.