Heat butter and oil in a skillet. Add mushrooms and sauté 7 minutes until tender.
Stir in the cream and grated cheese, season mixture and remove from heat .
Cut a slit in the top of the Lyonnaise and fill them with the mixture thoroughly.
Put them in a preheated oven and bake tray at 200 ° C for a few minutes to warm well .
Serve Lyonnaise .