Preheat and Prepare: Preheat your oven to 180°C (160°C fan). Lightly grease a 23x33cm (9x13 inch) baking dish.

Cook the Aromatics: Heat a large frying pan over a medium heat. Add the finely diced onion and cook for 4-5 minutes until it has softened and become translucent. Add the minced garlic and cook for another minute until fragrant.

Brown the Beef: Add the beef mince to the pan. Use a wooden spoon to break it up as it cooks. Brown the meat for 5-7 minutes until no pink remains. Drain off any excess fat from the pan.

Season the Filling: Stir the Worcestershire sauce, salt, and pepper into the cooked beef mixture. Take it off the heat and set aside. While that cools slightly, mix the mayonnaise, ketchup, mustard, and chopped gherkins in a small bowl to create the burger sauce.

Prepare the Buns: Take your slab of slider buns and, without separating them, use a large serrated knife to slice the entire block in half horizontally. Place the bottom half into your prepared baking dish.

Assemble the Sliders: Spread the burger sauce evenly over the bottom layer of buns. Next, spoon the beef mixture over the sauce, pressing it down gently into an even layer. Lay the cheddar cheese slices on top of the beef, ensuring it's fully covered. Place the top half of the buns back on.

Add the Topping: In a small bowl, mix the melted butter with the garlic powder and chopped parsley. What works best for me is using a silicone pastry brush to spread this mixture generously over the tops of the buns. Sprinkle evenly with sesame seeds.

Bake to Perfection: Cover the dish with foil and bake for 10 minutes. Then, remove the foil and bake for another 8-10 minutes, or until the cheese is completely melted and bubbling, and the tops of the buns are golden brown.

Rest and Serve: Let the sliders rest in the dish for 5 minutes before serving. This helps them hold together. Use a sharp knife to cut along the lines of the individual buns and serve immediately.