To prepare the onions up to a day ahead,
assemble the dish without the Parmesan,
then chill. To serve, scatter with the cheese,
Heat the oven to 200C/fan 180C/gas 6. Peel and trim the roots of the onions but leave them whole. Cook in a large pan of
boiling water for 25 mins until tender, then drain, reserving a little cooking water.
Season the cream and mix in 2 tbsp of the onion water. When the onions are cool enough to handle, slice each in half through the root. Lay the onion halves, cut side down, in a large baking dish with the bay leaves. Pour over the cream, scatter with the Parmesan, and bake for 25 mins until the cream is bubbling and the onions are just beginning to brown.