Preheat to 170°C fan bake. Line a roasting dish or sheet pan with baking paper.
Slice the rolls horizontally without separating the buns. You should now have a connected top layer and bottom layer.
In a small bowl, combine the mayonnaise, mustard, garlic powder and onion powder. Spread half over the bottom buns and half over the tops.
Lay ham over the bottom slab of buns. Add the Swiss cheese slices on top, making sure the cheese covers the fillings.
Bake the bottom slab (without the top buns) for 5–8 minutes to start melting the cheese.
To make the butter topping: Mix the melted butter, Worcestershire sauce, chives, salt, pepper and optional poppy seeds.
Remove the tray from the oven. Place the top buns on and spoon the butter mixture evenly across the top.
Cover with foil and bake for 10–15 minutes. Bake until the tops are crisp. Ensure the sliders are heated through. (You can remove the foil for the last couple of minutes for extra crispiness, but I found it didn’t need it).
Slice and enjoy warm — perfect for quick lunches, picnics and after-Christmas grazing platters.