Preheat your oven to its lowest setting and pop the loaf of bread in to warm through. Spend a few minutes gently brushing along the underside of the mushrooms to get rid of any bugs and dirt that might be hiding there. This is well worth the effort. Finely chop your parsley, stalks and all, reserving a few of the leaves.
Put the butter into a large hot pan and as soon as it starts to melt add a drizzle of olive oil, the mushrooms, sliced onion and a good pinch of salt and pepper. Stir everything around and cook for about 8 minutes, or until the onions have softened and the mushrooms are starting to caramelise and take on colour.
Add the chopped parsley, then pour in the cream. Continue to stir and cook for another minute, until the cream has come to the boil, then turn down the heat and simmer for a minute before removing from the heat. Add a good squeeze of lemon juice, have a taste, and add more salt, pepper or lemon juice if it needs it. Take your bread out of the oven and tear it into big chunks. Divide the mushrooms between your plates and scatter over the reserved parsley leaves. Serve with your chunks of bread on the side to mop up all the creamy mushroomy juices, and tuck in!