In a large frying pan, cook mushrooms in oil. When golden brown, add the onion and garlic and cook for a further 2 minutes.
Add the stock cube along with the small glass of wine. Simmer for a further 5 minutes. Turn to a medium heat, add creme fraiche and cream. Bring to boil, then reduce heat back down to a simmer for 2 minutes.
Place the toasted baguette on a serving plate. Top the slices with the creamy mushroom mixture, then sprinkle with parsley and black pepper to taste.