For the Aioli:
Combine mayonnaise, Monini Rosemary Flavored Olive Oil, and garlic together. Refrigerate 30 minutes
For the Onions:
Melt butter in a skillet over medium low heat and add your onions into the pan. Place a lid on the pan and leave for 20 minutes, stirring once or twice. Remove lid then cook for a further 20 minutes, stirring every now and then, until the onion is golden. Add sugar, vinegar, salt and pepper. Cook for a further 10 minutes until jammy. Remove from heat and keep warm.
Meat:
Let beef sit out for 20 minutes before cooking. Season generously with salt and pepper.
Heat Monini Originale Extra Virgin Olive 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 thinly against the grain.
ASSEMBLE SANDWICH
Cut ciabatta split into half. Toast lightly.
Spread the bottom piece generously with rosemary aioli. Top with arugula, then tomato slices, beef, caramelized onion. Spread the top piece of bread with mustard then place on top.