Bring a pan of water to the boil. Plunge the tomatoes into the boiling water for a few minutes and remove using a slotted spoon. Peel and de-seed the tomatoes and cut the flesh into small, even-sized cubes. 

Set aside.

Wash, de-stem and finely chop the mushrooms. Peel and chop the shallots. 

Melt the 50g of butter in a large, lidded frying pan. Lightly brown the shallots over a medium heat, stirring constantly with a wooden spoon. 

Add the diced tomatoes and wine. Cover and simmer over a gentle heat for 15 minutes. 

Add the mushrooms.

Cook over a medium heat for 5 minutes. Season with salt and pepper.

Place the salmon fillets carefully on top of the mixture. Cover and simmer for 15 minutes over a low heat. 

Sprinkle with chopped tarragon and serve.