Cardoon Gratin with Bone Marrow

Strip the stringy fibres from each cardoon piece as you would celery, pulling the strings from the outer edge. Rub the cut surfaces immediately with lemon juice to prevent browning. Fill a large pot with 4 litres of cold water and whisk in the 2 tbsp flour, lemon juice, and 1 tsp salt to make a blanc.

Bring the blanc to a boil over high heat, add the cardoon pieces, reduce to a steady simmer, and cook for 35 minutes until a knife slides through without resistance. Drain, rinse under cold water, and set aside on a clean towel.

Soak the bone marrow rounds in a bowl of lightly salted iced water for 20 minutes to draw out any blood, then drain and pat dry.

Stud the onion halves with the cloves. Combine the warmed milk, beef stock, studded onion, and bay leaf in a saucepan over medium-low heat and steep for 10 minutes without boiling. Remove the onion and bay leaf and discard.

Melt the butter in a heavy saucepan over medium heat until foaming subsides. Add the 50g flour and stir constantly with a wooden spoon for 2 minutes until the roux smells faintly nutty but remains pale.

Remove the pan from the heat and pour in the infused milk mixture in a steady stream, whisking vigorously to prevent lumps. Return to medium heat and cook, stirring constantly, for 8 minutes until the sauce thickens enough to coat the back of a spoon.

Remove the béchamel from the heat, stir in 80g of the Gruyère, all the Parmesan, the white pepper, and a generous grating of nutmeg. Taste and adjust salt.

Preheat the oven to 200°C, or 180°C for a fan oven, or gas mark 6. Butter a 30cm oval gratin dish generously.

Arrange half the cardoon pieces in a single overlapping layer in the dish. Distribute half the bone marrow rounds evenly across the cardoons. Spoon over half the béchamel. Repeat with the remaining cardoons, marrow, and béchamel, finishing with a smooth layer of sauce.

Scatter the remaining 40g Gruyère evenly over the top. Transfer to the oven and bake for 25 minutes until the surface is deeply golden and bubbling at the edges and the internal temperature of the gratin reads at least 75°C on an instant-read thermometer.

Rest the gratin for 5 minutes before serving, then scatter with the chopped parsley.