Mix the flour and salt in a bowl, create a well in the middle. Combine the milky water, eggs and saffron, gradually pour into the well while stirring, then mix with a risotto spoon and beat until the dough turns glossy and starts to bubble. Cover and leave to stand at room temperature for approx. 30 mins.
Press the dough in batches through a spaetzle sieve into the simmering salted water. Cook the spaetzle until they float to the surface, remove with a slotted spoon, drain, keep warm.
Heat the oil in a frying pan, fry the garlic and mushrooms for approx. 3 mins., leave to cool. Mix in the walnuts and all the other ingredients up to and including the salt.
Remove the meat from the fridge approx. 1 hr. before cooking, place on a plate.
Cook for approx. 80 mins. in the centre of an oven preheated to 80°C. The core temperature should be approx. 50°C.
Remove the meat from the oven, heat the oil in a frying pan. Fry the tenderloin on all sides for approx. 4 mins. Remove, spread the pesto on top, serve with fleur de sel.