Heat the olive oil and butter in a heavy-based deep saucepan over medium heat. When sizzling, add the onions. Immediately reduce the heat to low and cook for 45 minutes – 1 hours, stirring occasionally.
Once the onions are golden brown, season with a generous amount of salt and drizzle with balsamic glaze. Cook for a further 15 minutes, stirring occasionally. Set to the side.
Potato chips
Using a mandolin, finely slice the potatoes. Place them into a large bowl filled with ice water and leave to sit for a minimum of 30 minutes. Drain and pat dry with paper towels.
Heat the vegetable oil in a large pot to 190 degrees Celsius. Working in batches and using a slotted spoon, carefully place the potatoes into the hot oil and cook for 8 – 10 minutes or until golden brown. Remove from the hot oil with a slotted spoon and place onto a cooling rack. Repeat until all chips have been cooked.
Place the potato chips into a bowl and toss through with lots of flakey sea salt.
Garlic Butter
Preheat the oven to 200 degrees Celsius.
Using a sharp knife, slice the top off the garlic bulb, about 2 – 3cm down from the top to expose the raw cloves. Place into a small baking tray or sheet of alfoil and drizzle with olive oil and season with salt and pepper. Cover and bake for 1 hour.
Leave the garlic to slightly cool or until you are able to handle it. Using your fingers, squeeze the roasted garlic out of their skin.
Place the garlic into a bowl with the remaining ingredient and combine well with a fork. Set to the side until ready for use.
Chimichurri
Place all ingredients into a bowl and stir to combine. Taste and season to your liking. Leave to sit for a minimum of 15 minutes to allow the flavours to combine.
Set to the side and store any leftovers in an airtight container for up to 1 week in the fridge.
Steak
Bring the steak to room temperature by taking it out of the fridge at least 1 hour before cooking it. Season well with salt and pepper. Pat the seasoning into the steak.
On a very high heat, bring a cast iron pan to heat and drizzle with olive oil. When there is a slight haze coming from the pan, place your steak into it. Cook for 2 - 2.5 minutes until you get a golden and caramalised crust. Turn the steak over and cook for 2 minutes. After 45 - 60 seconds, toss in the garlic, butter, thyme and rosemary. Allow the butter to melt and baste the steak with the butter while it continues to cook.
Take the steak off the pan and transfer to a cutting board. Leave to rest for 5 - 10 minutes.
While the steak is resting, spoon a tablespoon of the garlic butter over the steak and drizzle with the leftover butter in the pan.
Sandwich
Spread the garlic butter onto each slice of the baguette and cook in a pan on a low – medium heat until toasted and golden brown. Assemble the sandwich by beginning with a layer of caramelised onions, followed by the slices of steak, then the pecorino romano, a tablespoon of chimichurri and lastly a handful of potato chips.
Top with the second piece of bread, cut in half and serve immediately.