Cut the baguettes into slices diagonally, about 2.5 cm (1 inch) thick. Place the slices on a baking sheet and brush with 2 tablespoons of the olive oil.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 4–5 minutes, until golden brown. Rub each slice with the whole garlic clove and keep the slices warm.
Heat the remaining oil in a frying pan and sauté the shallot and crushed garlic for 3–4 minutes, then add the mushrooms and cook them until they have released all of their juices. Stir in the chopped parsley and season with pepper.
Spoon the mushroom mixture on to the crostini and serve.