You need big flat field mushrooms for this. To prepare them, you cut out the central stalk and peel off the coarse outer skin.
Put them gill side up in an oven dish and spread with some garlic butter.
The stuffing is breadcrumbs mixed with grated Parmesan cheese, chopped pancetta or Parma ham, lemon zest and juice, chopped parsley, an egg and chopped spring onions, seasoned with pepper and a little salt (the pancetta and cheese are both salty).
You squeeze out the stuffing into balls and mould them on top of the mushrooms, drizzle over some olive oil and then bake them in a hot oven for around 25 minutes, until they are crisp and browned on top.
I like to serve these with some plain steamed spinach, but you can also serve them on top of split and toasted muffins or slices of sourdough toast.