Rinse and clean the broccoli, cut the roses into small pieces, peel the stems and cut them into pieces. Cut the chicory stems in half lengthwise, cut out the bitter stem from underneath in a cone shape. Briefly rinse the chicory.
In a large saucepan, bring enough salted water to a boil. In a baking dish, have ice-cold water ready. Cook the chicory stems in the salted water at high temperature for about 3 minutes. Lift out with a slotted spoon and drain well.
Next, cook the broccoli florets and stems in the boiling salted water until al dente, about 5 min, rinse in cold water and drain well.
Remove the skin from the onion and chop it very finely. Heat 1 tablespoon of the butter in a frying pan and sauté the onion cubes until soft. Add the breadcrumbs and the hazelnuts and fry briefly. Season with salt, pepper and cayenne pepper.
Preheat the oven to 200 degrees (convection oven 180 degrees).
Grease an ovenproof dish. Fill in the broccoli and the chicory in strips. Cut the cheese into small pieces and sprinkle half of it between the vegetables.
Rinse the cress and cut the leaves into small pieces with kitchen scissors. Sprinkle half of the cress leaves between the vegetables. Season with salt and pepper.
Spread the hazelnut and breadcrumb mixture evenly over the vegetables and sprinkle the remaining cheese on top. Place the gratin on the broiler in the oven (