Mix egg, flour, milk and 1 pinch of salt and let it swell for about 15 minutes. Wash the asparagus and cut off the woody ends. Cook in boiling salted water for 6-8 minutes until al dente. Peel and finely chop the onion. Chop the walnuts. Wash, clean and quarter the tomatoes, remove the core and dice the flesh. Chop the chervil finely.
Mix vinegar with salt, pepper, sugar and 5 tablespoons of water, add walnut oil. Stir in walnuts, onion and diced tomatoes. Remove the asparagus from the water, drain and marinate with the vinaigrette. Heat the oil in portions in a frying pan and fry 1/4 of the pastry at medium heat for about 3 minutes on each side until golden brown. Bake the rest of the dough in the same way. Put the crêpes on plates and fold them twice. Fill with the marinated asparagus