Chargrilled onglet and watercress sandwich with quick-pickled celeriac rémoulade

First quick-pickle the celeriac and butternut squash. Julienne the vegetables by cutting then into fine matchsticks, then cover with the pickling vinegar. Leave to quick-pickle for 15 minutes

In the meantime, make a dressing for the rémoulade. Whisk together the oil, mustard and a tablespoon of the vinegar from the celeriac until emulsified. Then stir in the capers and chopped herbs. Taste and season with lemon juice, salt and black pepper

Season the steak with a generous amount of salt and pepper. Place a large griddle pan over a high heat. (You may need to cut the steak in half to fit it all in at once.) When the pan is smoking hot, add a dash of oil and the steak. Cook on a medium-high heat for 3–4 minutes each side – depending on the thickness of the onglet, you may need to finish in the oven for 2–3 minutes for a medium-rare finish

Whilst the steak is resting in a warm place for at least 5 minutes, drain the celeriac and butternut squash, and stir through the dressing

Use the same griddle pan to toast the sourdough, as the bread will mop up some of the steak juices

Once it has rested, carve the onglet – make sure you are cutting against the grain, otherwise it will be stringy and chewy. Sprinkle with flaky sea salt then assemble the sandwiches

Spread mayonnaise over 4 of the pieces of toast, add the watercress then divide the steak between the sandwiches. Top with rémoulade and place on the lid. Serve immediately