Peel, wash, halve and slice the kohlrabi. Steam the kohlrabi in a closed pot with a little salt water for 8-12 minutes. Wash chicken legs and pat dry. Mix oil, paprika, salt and pepper and brush the chicken legs with it.
Melt the fat. Sweat flour in it. Add cream while stirring constantly, bring to the boil and simmer gently for about 5 minutes. Season to taste with salt and pepper. Grate the Gouda roughly and melt about 30 g in the sauce.
Wash the chives, dab dry and cut into fine rings. Add up to about 1 teaspoon to the béchamel. Quench the kohlrabi and let it drip off. Layer the kohlrabi in a greased casserole dish and pour the chives béchamel over them.
Sprinkle 40 g Gouda over the gratin. Line half of the fat pan of the oven with aluminium foil. Fold up the aluminium foil so that it forms a bowl. Put the legs in. Place the baking dish on the other half.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 30-35 minutes. Take everything out, arrange clubs on a plate. Garnish with chervil. Sprinkle remaining chives over the gratin.