Cut prepared vegetables into bite-sized pieces and blanch separately (depending on the vegetable) in boiling salted water until al dente. Remove from the water, rinse in cold water and drain well.
Peel onions and garlic and chop finely. Heat butter in a pan and saute onions and garlic until translucent. Add wine, vegetables and crème fraîche and season with salt and pepper. Spread mixture in a baking pan and sprinkle with Parmesan. Bake in preheated oven at 200°C (approximately 400°F) for about 25-30 minutes or until golden brown. Remove from the oven and serve.