In a bowl, combine the Mayonnaise, Tomato Ketchup, Chilli Sauce and Mustard. Mix well until smooth and set aside.

Divide the Beef into 8 equal portions and loosely shape into balls. Avoid compacting the meat too much, as this helps create tender patties.

Heat a large frying pan or griddle over high heat. Place the Brioche Toast Slices into the dry pan and toast on one side only until golden brown. Remove from the pan and set aside.

Spread a generous layer of the prepared sauce onto the toasted side of each slice of bread.

Place a Mozzarella Cheese Slice onto the sauced side of each bread slice and set aside while you cook the patties.

Return the pan to high heat. Place the Beef portions into the pan and immediately smash them into thin patties using a burger press, spatula or another heavy flat object.

Season the patties generously with Salt and Black Pepper.

Scatter the julienned Onion evenly over the patties. Press the onions gently into the meat and cook for 1 to 2 minutes until the underside develops a deep golden-brown crust.

Flip the patties and immediately place a Cheddar Cheese Slice on top of each one. Continue cooking for about 30 seconds, or until the cheese begins to melt.

Stack two patties together to create four double patties.

Place each double patty onto a prepared slice of bread. Top with another prepared slice, keeping the sauce and cheese facing inwards to form a sandwich.

Reduce the heat to medium-low. Place the sandwiches back into the pan and toast for 1 to 2 minutes until the underside is golden brown and the cheeses begin to melt together.

Carefully flip each Patty Melt and cook for a further 1 to 2 minutes until the second side is golden brown, crisp and the cheese is fully melted.

Remove from the pan, allow to rest for 1 minute, then slice and serve immediately.