For the sauce, melt the butter in a saucepan over medium heat, stir in the flour until smooth, then gradually mix (stirring constantly) with the cream and milk.
Stir in the yeast flakes, bring to a full boil once and remove from heat.
Season to taste with salt and pepper.
Layer the potatoes and mushrooms alternately in the dish.
Pour over the sauce and sprinkle with cheese.
Bake at 200 degrees convection oven for minimum 40 min.
Pro tip: if you cover the form with aluminum foil or a lid, the cheese melts especially well. Bon appetite!