Peel and finely dice 1 onion. Clean and wash the mushrooms, dab dry and cut into slices. Cut the sausages into slices as well and fry them all around in hot oil. Add the mushrooms and onion and fry. Add the vegetables without defrosting and steam for about 3 minutes while stirring.
Dust with flour and sauté. Add cream and stock, bring to the boil and cook over low heat for about 10 minutes. Season to taste with salt and pepper. In the meantime, bring 3/8 litres of water and salt to the boil and remove from the heat. Add milk, stir in puree flakes and let it swell for 1 minute. Stir again. Peel remaining onions and cut into rings. Fry in hot fat until crispy brown. Wash parsley, dab dry and chop. Add to the ragout.
Stir again. Peel remaining onions and cut into rings. Fry in hot fat until crispy brown. Wash parsley, dab dry and chop. Add to the ragout. Spread the ragout with mashed potatoes on four plates. Spread onion rings with fat over the mashed potatoes