1. Grease a casserole dish with a small amount of the butter.
2. Sautee the mushrooms in olive oil very gently, and make the sauce
using a gentle heat throughout.
3. Melt the butter in a large (preferably non-stick) saucepan,
then add flour and stir like crazy until it goes into a lump. Now
add about a quarter of a teacup of milk and stir like crazy again
until the mixture goes solid again.
Keep doing this, adding a small amount of milk and stirring like
crazy. Eventually, the mixture will begin to go saucy and more runny.
If it goes lumpy, stir even more crazily until they go away. Don't
add milk when you have lumpy sauce: stir them out first. Eventually,
you will have used up all the milk and you should hopefully be stirring
a decent white sauce. Add the bayleaf and let the sauce simmer for
five minutes or so, to allow it to cook. Then take it off the heat
and remove the bayleaf. Season the sauce with salt and pepper.
4. Once the mushrooms have softened, add them into the sauce. Grate
the cheese and stir into the sauce. Keep stirring until the cheese