preheat oven to 375 degrees
In a large skillet, heat the olive oil and butter. Add the onion and plenty of salt and pepper. Cook, stirring often until the onion softens.
Add the garlic, cook for about 30 seconds and then add the mushrooms. Cook for about 5 minutes or until the mushrooms lose their moisture. Pour the onion/mushroom/garlic mixture on a plate to cool.
In a bowl, combine the milk and breadcrumbs; stir with a fork.
In another bowl, combine the beef, pork, nutmeg, allspice, thyme, Worcestershire, eggs, cooled mushroom mixture, breadcrumbs, 1 tsp salt and 1/2 tsp pepper. Using your hands, mix quickly but thoroughly.
Spray a 9 x 13" baking dish with cooking spray. Transfer the mixture to the baking dish and form it into a squared off log, 6" wide and about 10" long.
Lay bacon sliecs across the top of the meatlof. It's okay if they hang down into the pan becuase they will shrink up with baking. Sprinkle the top of the bacon with brown sugar.
Bake the meatloaf for 50-55 minutes, or until the interior temperature registers 160 degrees. Rest for 5 minutes. Cut into thick slices
Note: don't overcook the meatloaf because the bacon doesn't look done. If you need to crisp up the bacon, turn on your broiler and watch closely just enough to crisp it. I highly recommend using a meat thermometer so you don't dry it out.