Clean and finely dice the mushrooms. Rinse and dry the parsley, then coarsely chop the leaves. Peel and finely chop the shallot and garlic. Heat the oil in a pan, add the mushrooms, and cook for 5 minutes until golden brown and the liquid released has evaporated. Remove from the pan and let cool. Mix the mushrooms with the crème fraîche and half of the parsley. Season to taste with salt and pepper, then spread on the slices of bread. Garnish with the remaining parsley and serve.