Preheat the oven to 180°C.
Remove mushroom stalks and reserve for the filling.
Drizzle mushrooms with 30ml olive oil and season with salt and pepper.
Sear mushrooms gill-side down in a hot griddle pan until golden-brown.
Fry chopped onion and garlic in the remaining oil for five minutes.
Add chopped stalks and bacon to the pan and fry for five minutes.
Deglaze with white wine and simmer until reduced.
Stir in the cream and half of the cheese.
Stuff the mushrooms with the mixture and top with remaining cheese and sage.
Bake on a tray for 6-8 minutes until the cheese browns.