Preheat the oven to 350℉.

Place onion, ground beef, salt, pepper, onion soup mix, and milk into a large bowl and mix with your hands until everything is completely combined.

Pour the hamburger mixture into a 9x13-inch casserole dish. Pressing down firmly, push the hamburger down flat so that it touches all sides of the dish.

Place the dish in the oven and bake for 20 minutes.

While the hamburger is baking, prepare another casserole dish by spraying it with cooking spray and set aside.

Without taking the dinner rolls apart, cut them lengthwise, hamburger-style. Place the bottom half of the dinner rolls into the casserole dish.

Next, layer 5 slices of cheddar across the rolls completely covering the whole surface.

When you take it out of the oven it should shrink about 25%, loosing about an inch at each end of the hamburger. Take the hamburger out of the casserole dish and drain or pat off the extra oil and juices that may have settled on the top. Do not turn the oven off yet.

Place the giant hamburger patty on top of the first layer of cheese. Then place the rest of the cheese across the top and place the top of the dinner rolls on top of the cheese.

Brush the melted butter across the top of the rolls and sprinkle with sesame seeds.

Place the sliders back into the oven and bake for 20 more minutes.

Let rest for 5 minutes before cutting and serving.