Preheat oven to 350˚F. Butter the bottom of a rimmed baking sheet.

Place a large skillet over medium/high heat with ½ tablespoon olive oil. Add diced onion then 2 lbs ground beef and break up with a spatula. Season with 1 teaspoon salt, 1 teaspoon black pepper, and 1 teaspoon garlic powder. Sautee over medium/high heat, breaking up the beef and cook just until cooked through then remove from heat.

Tilt skillet to spoon off and discard excess fat. Stir ¼ cup mayo into the ground beef.

Cut buns in half. Place bottom half of dinner rolls on buttered baking sheet and line bread with sliced cheese. Spread ground beef mixture evenly over the sliced cheese, using the back of a spatula to square off the edges. Cover the ground beef with 6 oz of shredded cheddar.

Place the top of buns, cut-side down, over the burgers. Brush tops with 2 tablespoon melted butter and immediately sprinkle tops with sesame seeds. Bake at 350˚F for 12-15 minutes, or until cheese is melted and tops are golden brown.