Gratín de papas trufado con champiñones asados

potato 60.0% , cream 21.5% , milk 9.2% , butter 4.6% , olive oil 2.3% , parmigiano reggiano 1.2% , salt 0.5% , Modified starch 0.3% , onion 0.2% , garlic 0.1% , extra virgin olive oil 0.0% , rosemary 0.0% , bay leaf 0.0% , black pepper 0.0%