Pre-heat oven to 350, dice your onion, and butter the bottom of a rimmed baking tray.
In skillet over medium/high heat add your oil and diced onion. Sauté/stir onion until brown and caramelized.
Add ground beef and season to taste with salt and pepper. Break the beef up and cook until it’s no longer pink and remove from heat. Discard any excess oil or fat. Stir in the mayonnaise and set aside.
Cut the dinner rolls or slider buns in half. Put the bottom half of the rolls on the baking tray and add the slices of cheese.
Layer the ground beef mixture on top of the cheese slices. Top with shredded cheddar cheese and put the top half of the rolls on.
Brush the tops of the buns with melted butter and add sesame seeds (optional)
Bake at 350 for 10-15 minutes until cheese is melted and tops are golden color.
