Make the pickled red onions at least 1 hours in advance to get the maximum flavour and for the colour to develop into a lovely pink pickle. 
Peel and thinly slice the red onion using a knife or a mandolin if you have it.

Juice the lemons into a bowl with the onions and season with sea salt. Stir to combine until the onions are mostly submerged in the juice. Allow to sit at room temperature until ready to use. These can be stored in a jar in the fridge for up to a week.

Make the spicy mayo by stirring together the mayonnaise and hot sauce and set aside.

Next get started on the chips. Wash and cut the potatoes into chips.

Place the chips in a large, heavy-based pot or casserole dish and pour over the sunflower oil until it covers them. Place over a high heat and bring to a steady boil. Reduce the heat to medium and cook for 10 minutes before gently moving with tongs to loosen any that are stuck to the base. Continue to cook for a further 10 minutes or so or until they turn golden-brown.

Remove with a slotted spoon to a baking tray lined with parchment paper. Season generously with sea salt.

While the chips cook, work on the burger: add the minced beef, Dijon, Worcestershire sauce, garlic, ketchup, thyme, salt and pepper to a large bowl and mix until everything is evenly combined.

Divide into 4 and shape into patties.

Place a large pan on a medium high heat and add the oil. Fry the pancetta for 2-3 minutes on either side or until nice and crisp, set aside.

Reduce the heat to medium and place the burger patties in the pan, fry for 6 minutes on either side or until cooked through and browned.

Once cooked, top with the cheese and cover with a cloche or lid for 3-4 minutes until the cheese is oozing and melted.

Place the bottom of the toasted bun onto a plate, smear with the spicy mayo, top with the burger, crisp streaky pancetta, pickled red onion and rocket followed by the burger bun top. Serve along with the crispy homemade fries.