Preheat your oven to 180C
Peel and dice the onions. Peel and finely slice the garlic, then place in a large casserole pan on a medium-low heat with 1 tablespoon of olive oil.
Strip in the thyme and cook for 10 minutes, stirring regularly, while you slice the mushrooms and tear the bread into 4cm chunks.
Stir the mushrooms into the pan, pour in the stock and bring to a boil.
Add the bread, then grate in most of the cheese. Stir well, grate over the remainder of the cheese, and transfer to the oven for 25 minutes, or until dark golden and very thick.
Season to perfection, then serve drizzled with extra virgin olive oil.