Make the Cheeseburger Sliders:

Preheat the Oven:

• Arrange a rack in the middle of the oven and preheat it to 350°F.

Cook the Onions:

• Halve and thinly slice 1 medium yellow or red onion (about 2 cups).
• Grate 6 ounces of medium cheddar cheese (about 1 1/2 cups).
• Heat 2 teaspoons of the neutral oil in a large skillet over high heat until shimmering.
• Add the onions and cook until charred in spots, about 4 to 6 minutes. Transfer the onions to a plate and set aside.

Cook the Beef:

• Reduce the heat to medium-high and add the remaining 1 teaspoon of oil to the pan.
• Add 1 pound of ground beef and cook, breaking it up with a wooden spoon into small pieces, until cooked through, about 5 minutes.
• Stir in 2 tablespoons of mustard, 2 teaspoons of Worcestershire sauce, 1/2 teaspoon garlic powder, 1/2 teaspoon kosher salt, and 1/4 teaspoon black pepper.
• Cook, stirring constantly, until browned in spots, about 2 minutes. Remove from heat.

Assemble the Sliders:

• Without separating the rolls, cut the package of Hawaiian sweet rolls in half horizontally using a serrated knife.
• Place the bottom half of the rolls in a small rimmed baking sheet (11x7-inch) or a 9x13-inch baking dish.
• Layer 8 slices of American cheese evenly over the bottom half of the rolls, overlapping as needed.
• Top with the cooked onions, followed by the beef mixture.
• Sprinkle with the shredded cheddar cheese and add 1/2 cup sliced dill pickles.
• Place the top half of the rolls over the pickles, cut-side down.

Bake the Sliders:

• Brush 1 tablespoon of melted butter or olive oil over the top of the rolls and sprinkle with 2 teaspoons of sesame seeds.
• Cover the dish tightly with aluminum foil and bake for 10 minutes.
• Uncover and bake for an additional 12 to 15 minutes until the cheese is melted and the bun tops are toasted.

Make the Burger Sauce:

Prepare the Sauce:

• In a small bowl, combine 1/2 cup mayonnaise, 1/4 cup ketchup, 2 tablespoons sweet pickle relish, and 1 tablespoon yellow mustard.
• Stir to combine and taste. Add up to 1 more tablespoon of mustard, kosher salt, and black pepper as needed.

Serve:

• Serve the burger sauce alongside the sliders for dipping.