Celeriac in salty crust

Place a cheesecloth in a sieve and pour in the buttermilk. Leave the buttermilk covered in the refrigerator to drain overnight and collect the moisture. Then reduce the liquid in about 30 minutes to a nice sauce thickness.

Preheat the oven to 200 degrees. Mix the salt with water to a kind of sticky mass. Put the celeriac in an oven dish in a layer of salt and then cover the tuber completely under the salt, it will cook in the oven for about 3 hours. Turn off the oven and let the celeriac stand overnight. Then tap the celeriac out of the salt and brush off any leftover salt.

Finely chop 5 1/2 white onions. Heat a pan with 2 tbsp. oil, add the finely chopped onions, a little salt and sherry vinegar and let it cook for about 5 hours on a low heat below the boiling point until it becomes a kind of sweet caramelized chutney.

Heat the oven to grill setting. Cut the remaining half white onion into wafer-thin slices, drizzle with some oil and grill until the edges turn black.

Cut off the skin of the celeriac, halve and cut into 8 slices. Place the celeriac slices in a baking dish, spoon over some of the onion compote, grate over the Gouda cheese spread, sprinkle with lemon thyme and au gratin under a hot grill. Heat the buttermilk sauce and assemble it by adding butter and whisking with an immersion blender until fluffy. Season with salt and pepper.

Spoon 2 slices of celeriac on 4 plates, and add some of the buttermilk foam with a spoon. Serve with optional. some herb salad to make it a bit fresher.