Garlic Aioli: Mix mayonnaise and garlic together. Set aside for 30 minutes+ for the flavour to develop (do not keep for more than 3 days tops).

Caramelised Onion: Melt butter in a skillet over medium low heat. Add onions and stir to coat in butter. Place lid on (or place a baking tray over skillet) and leave for 20 minutes, stirring once or twice. Remove lid then cook for a further 20 minutes, stirring every now and then, until onion is golden (increase heat slightly if the colour is not changing). Add sugar, vinegar, salt and pepper. Cook for a further 10 minutes until jammy. Remove from heat and keep warm.

Take beef out of fridge 20 minutes before cooking. Season generously with salt and pepper.

Heat oil in a skillet over high heat (or heat BBQ). Cook steak to your liking - if using a secondary cut like Bavette, skirt or flat iron, it's best medium rare.

Transfer beef to a plate, cover loosely with foil and rest for 5 - 10 minutes. Then slice thinlyagainst the grain.

Cut turkish bread into 15cm/6" lengths and split into half. Toast lightly.

Spread the bottom piece generously with garlic aioli. Top with rocket, then tomato slices, beef, caramelised onion. Spread the top piece of bread with mustard then place on top.