For the soubise sauce, finely grate the onion into a bowl, collecting the juices. Melt 20g butter in a small saucepan over medium heat. Cook the onion for 15 minutes or until caramelised, stirring regularly.

Add the remaining butter to the pan. Once melted, add the flour and cook for one minute. Gradually whisk in the milk until thickened. Season with salt and pepper. Remove from the heat and keep warm.

For steak: Lightly bash the steak with a rolling pin or meat mallet to tenderise. Season both sides with salt and pepper. Heat a frying pan over medium-high heat and cook the steak to your liking. Remove and set aside for five minutes to rest.

Fry the bacon for three minutes each side or until golden. Remove and keep warm. Reduce the heat to medium and wipe the pan clean. Spread the buns with butter and scatter with the cheese, pressing firmly down.

Fry the buns, cheese side down, for 1-2 minutes until the cheese is toasted.

Thinly slice the steak on an angle. Top each bun with the steak and pour over a quarter of the soubise sauce.

Add the bacon and watercress and serve.