In a saucepan heat the butter and saute the onion. Stir in the rice and the blueberries, saute briefly. Moisten with wine, cook until absorbed; moisten with bouillon and cook until tender. Stir continuously, if necessary add some bouillon. Season with salt and pepper. In a skillet heat the oil, saute mushrooms, garlic and thyme. Stir the butter into the risotto. Transfer to warm plates and decorates with mushrooms.