01 -
Heat a large skillet over medium-high heat. Add diced onion and ground beef, then season with beef bouillon powder, salt, and pepper. Cook, breaking up the meat, until beef is browned and onion is translucent.
02 -
Stir in minced garlic and cook for 30 seconds, just until fragrant. Avoid letting the garlic brown.
03 -
Pour off any excess grease from the skillet, leaving the beef and onion mixture lean but juicy.
04 -
Add tomato sauce, ketchup, mustard, Worcestershire sauce, brown sugar, onion powder, and garlic powder. Stir the mixture thoroughly to combine.
05 -
Bring the mixture to a simmer and cook for 5 minutes, stirring occasionally, until the sauce thickens to a spoonable consistency. Remove from heat and let the filling cool slightly.
06 -
Place a clean skillet or griddle over medium heat, allowing it to come up to temperature while assembling sandwiches.
07 -
Spread mayonnaise evenly over one side of each bread slice. Lay four slices mayo-side down on a work surface.
08 -
Top each bread slice on the work surface with one slice of cheese, a generous scoop of sloppy joe filling, and a second slice of cheese. Cover with remaining bread slices, mayo-side up.
09 -
Place sandwiches onto the preheated skillet. Cook until the bottom is golden and crisp, about 3–4 minutes, pressing gently with a spatula.
10 -
Carefully flip each sandwich and cook the second side until golden and cheese is fully melted, 2–3 minutes more. Remove to a board, rest for 1 minute, then slice and serve hot.