Preparation time: 20 minutes plus chilling
Cooking time: 30-35 minutes

1 head of garlic, unpeeled
1 tsp olive oil
1 (85g) bag watercress
675g/11/2lb lean minced beef
15ml/1 tbsp Dijon mustard
salt and freshly ground black pepper
4 buns
For the watercress butter:
1 (85g) bag watercress
100g/4oz unsalted butter
1 shallot finely chopped
2 anchovy fillets
30ml/2 tbsp ground almonds

Preheat the oven to 180°C/Fan 160°C/Gas Mark 4. Cut the top off the bulb of garlic and drizzle over the olive oil, bake for 20 mins or until the garlic is tender. Cool, separate the cloves of garlic and squeeze the pulp from each: place in a bowl.

Whilst the garlic roasts, make the butter: finely chop the watercress and mash into the butter with the shallot, anchovy and almonds. Season with pepper. Roll the butter in greaseproof paper to form a sausage shape. Freeze for 20 mins.

To make the burgers, finely chop half the remaining watercress and mix with the garlic, mince and mustard. Season with a little salt and plenty of ground black pepper. Divide the mince into four and shape into a 2.5cm/1in thick burgers. Divide the butter into four, make an indentation in each burger, place a nugget of butter at the centre then shape the mince to enclose the butter inside the burger. Chill until ready to cook.

Grill, pan-fry, griddle or barbecue the burgers to your liking, turning once: 4 mins each side for rare; 6 mins each side for medium; 8 mins each side for well done. Set aside to stand for 5 mins.

Split the buns and toast the insides. Fill with the burgers and remaining watercress leaves.