Caramelise the Onions: Heat the olive oil and 1 tbsp of butter in a large frying pan over a medium-low heat. Add the sliced onions and cook slowly for 15-20 minutes, stirring occasionally, until they are soft, sweet, and golden brown. Knowing how to caramelise onions properly is a great kitchen skill. Once done, remove them from the pan and set aside.

Prepare the Au Jus: In the same pan, add the 500ml of beef stock, 1 tbsp Worcestershire sauce, onion powder, and garlic powder. Bring to a simmer over a medium heat, scraping up any browned bits from the bottom of the pan. Let it simmer gently for at least 10 minutes to allow the flavours to deepen. Season with black pepper.

Warm the Beef: Add the thinly sliced roast beef to the simmering au jus. You only need to warm it through for 1-2 minutes. Using tongs, remove the beef from the jus, letting any excess liquid drip off, and place it in a bowl. Keep the au jus simmering gently on a low heat.

Assemble the Buns: Preheat your oven to 180°C (160°C fan). Slice the sheet of slider buns in half horizontally without separating them. Place the bottom half in a baking dish. I find that lightly toasting the cut side under the grill for a minute at this stage helps prevent a soggy bottom.

Layer the Sliders: Layer the warmed beef evenly over the bottom buns. Top with the caramelised onions, spreading them out, followed by the slices of Provolone cheese. Place the top half of the buns back on.

Make the Topping: In a small bowl, whisk together the 60g of melted butter, 1 tbsp Worcestershire sauce, Dijon mustard, garlic powder, and chopped parsley.

Bake the Sliders: Brush the butter mixture generously over the tops of the buns, ensuring they are fully coated. Cover the baking dish loosely with foil and bake for 10-12 minutes.

Final Browning: Remove the foil and bake for another 5-7 minutes, or until the tops are golden brown and the cheese is bubbling and completely melted.

Rest and Serve: Let the sliders rest for a few minutes before slicing them into individual portions. Serve immediately with the warm au jus on the side for dipping.