Line the glass loaf pan with the bacon, centering the strips lengthwise in the pan, letting the ends hang over the short edge.
Lightly beat the eggs in a large bowl. Add the ketchup and sour cream and mix. Add the breadcrumbs, onions and garlic, stirring to incorporate, and sprinkle with salt and pepper. Mix in the sausage, breaking it up to season the egg mixture evenly. Mix in the ground beef, using your hands to mix gently but thoroughly. Press the meatloaf mixture firmly into the loaf pan with the bacon, shaping the meat into a loaf shape. Unmold the meatloaf by turning the pan upside-down, and tapping the bottom to release the meatloaf. Tuck the bacon under the loaf, and place it bacon-side up on a foiled or parchment-lined baking sheet. Bake until the meat registers 160 degrees F, 50 minutes. Let rest 10 minutes before slicing. Serve with Mustard and Sour Cream Gravy.
Mustard and Sour Cream Gravy:
In a saucepan, heat the butter over medium heat, add the onions and saute until the onions are soft, about 6 minutes. Sprinkle the flour on top of the onions and cook for 1 minute, stirring. Turn up the heat to medium-high and whisk in the stock and 1/2 cup water. Cook at a simmer, whisking frequently, until the gravy begins to thicken. Turn off the heat and whisk in the sour cream, and then the mustard and Worcestershire sauce. Taste before adding salt and pepper. Serve on the meatloaf.