01 -
Preheat oven to 204°C. Lightly coat a 1.9 L baking dish with olive oil spray.
02 -
Heat olive oil in a large skillet over medium-high heat for 2 minutes. Add chopped onions and ground beef.
03 -
Cook, breaking up the beef and stirring until the beef is browned and onions are tender, approximately 5 minutes. Drain excess liquid if present, then return mixture to skillet.
04 -
Add black pepper, minced garlic, and kosher salt to the skillet. Stir and cook for several minutes to combine flavors.
05 -
Remove skillet from heat. Stir in unsweetened ketchup, mayonnaise, mustard, and 113 g (1 cup) of shredded cheddar cheese until evenly mixed.
06 -
Transfer the mixture evenly into the prepared baking dish and evenly sprinkle with the remaining cheddar cheese.
07 -
Bake in the preheated oven for 15 minutes until the cheese is melted and the dish is heated through.
08 -
If the baking dish is broiler-safe, place under broiler 15 cm from the heating element for 1–2 minutes until cheese is melted and lightly browned.