Preheat your oven to 400°F (200°C). In a small bowl, mash the softened butter and minced garlic together. Spread evenly over the cut sides of your halved French bread. Bake for 5-7 minutes until the bread becomes toasted and crispy on top.

Heat a large skillet over medium-high heat. Add the lean ground beef and diced yellow onion. Cook for 6-8 minutes until the beef develops a deep brown crust and onions are translucent. Drain excess grease.

Reduce heat to medium-low. Stir the tomato paste into the beef, cooking for 1 minute. Pour in ketchup, Worcestershire sauce, brown sugar, mustard, salt, and pepper. Simmer for 3-5 minutes until the sauce is thick and glossy.

Switch the oven to the Broil setting. Carefully spoon the thick sloppy joe mixture evenly over both toasted French bread halves. Sprinkle the mozzarella and cheddar cheese heavily over the meat in an even layer.

Place the loaded bread under the broiler for 2-4 minutes. Watch carefully until a thick layer of melted, bubbly, slightly golden-brown cheese forms. Remove from the oven.

Let the bread rest on a rustic wooden cutting board for 3 minutes. Garnish generously with the finely chopped fresh green parsley. Cut into thick slices and serve immediately.