Cut the salmon transversely into about 10 equally sized cubes. Melt butter in a small pot. Season with lemon zest and 1 pinch of cayenne pepper
Season salmon with a little salt. Spread some lemon butter on an ovenproof plate, place the salmon pieces on top, leaving a distance of about 2 cm between the cubes. Brush generously with the lemon butter from all sides. Cover with cling film. Cook in the preheated oven (electric cooker: 100 °C/ convection oven: 75 °C/ gas: see manufacturer) for approx. 20 minutes until translucent
For the soup, peel the shallots, dice them finely and sauté them in the olive oil in a pot until translucent. Cut the tomatoes into cubes, removing the stalk. Add to the shallots and briefly sauté. Fill up with white wine and stock. Add peeled garlic clove and thyme. Cover and simmer for about 15 minutes.
4 . Then remove the thyme and garlic again and puree the soup finely with a hand blender. Pour through a sieve and reheat in a pot. Season to taste with saffron threads, salt and pepper. Add cream and bring the soup to the boil
Shortly before serving, mix with a hand blender until foamy. Arrange the soup with as much foam as possible and lukewarm salmon and serve immediately