Peel the celeriac twice: the skin is thick and, as with turnips, it often needs peeling a second time.

Grate the celeriac.

Peel the apple and cut it into cubes, then chop the parsley.

Boil some water.

In a large bowl, pour in the tahini, the grated lemon zest and juice, the cider vinegar, the agave syrup, the olive oil and 1 tsp of salt, then whisk together.

Pour in the boiling water little by little in a thin stream while whisking, until the sauce is smooth.

Add the celeriac, apple and parsley, mix together and serve immediately or keep in the refrigerator.