Dice the Beaufort and slice the onions and mushrooms. Keep a few onion slices to one side for decoration.
Mix the flour and salt in a bowl.
Stir the water into the yeast and add to the bowl.
Blend with the spatula for 2 minutes and add the onions, mushrooms and diced Beaufort. Mix again until you have a smooth dough and finish by kneading with a rolling pin.
Shape the dough into a ball, put it back in the bowl and cover with a cloth. Leave to rest for 45 minutes in a warm place.
Take the ball of dough, divide it into 2 equal pieces and leave to rest, covered, for 10 minutes. Shape into 2 balls, place them on a baking sheet and leave to rest, covered, for 45 minutes.
With the aid of a knife, make a cross on the top of the loaves, brush them with water and arrange 4 onion slices on top.
Put the loaves in an oven pre-heated to 230°C and bake for 35 minutes.