Preheat the oven to 180°C fan bake.
Heat the olive oil and butter in a large frying pan and cook the pancetta for 5 minutes, until crispy and golden.
Remove from the pan and set aside.
Add the onion to the fat remaining in the pan and cook over a gentle heat for 10 minutes.
Remove from the pan and add to the pancetta.
If necessary, add 1 or 2 more tablespoons of oil to the pan, season the mushrooms well with salt and pepper, then cook over a medium-high heat for 10 minutes, stirring occasionally to stop them from catching.
While the mushrooms are cooking, boil the gnocchi according to the packet instructions, then drain well.
Add the pancetta and onions to the mushrooms along with the wine and cream and cook together for 5 minutes.
Add the gnocchi to the mushrooms with half of the brie and stir to combine, then spoon into an ovenproof dish and top with the remaining brie and the walnuts.
Finish in the oven for 10-15 minutes before serving with a simple bitter green salad or freshly cooked green beans.
