1 Set the oven to 160 degrees.

2 Cut the onions in half across the circumference. Drizzle the oil on a roasting tray, scatter the sprigs of thyme around, then place the cut side of the onion down on the tray, cover with foil and bake for 45 minutes.

3 Remove the onions and turn the oven up to 185 degrees.

4 Allow the onions to cool, then peel the outside layer off while keeping the shape of the onion.

5 Take a non-stick frying pan (big enough to accommodate the onions in one layer). Smear the base and sides with the butter, season and place the onions cut-side down on top of the butter.

6 Cut a circular piece of pastry the same size as the rim of the pan – it doesn’t have to be too perfect. Drape the pastry snugly over the top of the onions and tuck it in.

7 Brush the pastry lightly with the egg wash and bake for 25 minutes until crisp and golden.

8 Allow to cool for no more than a minute or two, then nudge the pastry away from the pan with a spatula and turn it out carefully, with the onions on top. Place on a tray to warm through when you’re ready to serve.

FOR THE HORSERADISH BUTTER:

Mix everything together. Roll in clingfilm and chill.

FOR THE BEEF:

1 Set the oven to 95 degrees.

2 Brush the meat with a little sunflower oil and season it. Place on a wire rack in the oven for about an hour and 45 minutes. The core temperature needs to be 60 degrees – this is at the cusp of medium rare to medium.

3 To sear it, heat a large pan with more oil over a high heat until lightly smoking. Gently lower the beef into the pan and cook for three minutes or so, until the beef is dark and crusted.

4 Turn the meat over and add the butter, thyme and garlic to the pan. Baste the steak three or four times. When the crust has formed on the second side, transfer to a board.

5 Warm the onion tart, carve the meat, and serve with the horseradish butter.