Brush the chanterelles with a brush. Then sauté in a hot pan with a little olive oil and set aside.
Finely dice one part of the Le Gruyère AOP and cut the rest into thin square slices. Finely chop basil.
For the burger, place the veal mince in a bowl, add the Worcestershire sauce, a tablespoon of mustard, chopped basil, the Le Gruyère AOP cube, salt and pepper and mix well.
Form small meatballs and cook them in a hot pan (high heat).
Slice the bread rolls and top with the meatballs, Le Gruyère AOP slices, spinach leaves, chanterelles and 1/2 teaspoon of mustard. Finally cover with the upper half of the bread roll.