Place the haddock in a pan with the hot milk until the fish is completely covered. Cover and leave for 1 hour.
Heat the stock and saffron to a simmer.
Wash the spinach and wilt in boiling water for a few seconds. Cool in ice cold water, drain well, squeeze out the excess water and cut the spinach into strips.
Remove the fish from the milk, drain well, pat dry with kitchen paper and peel off the skin. Divide the fish into bite-size pieces.
Peel and finely chop the onion. Heat the butter in a pan and saute the onion until softened. Pour in the vinegar, saffron stock and white wine. Allow to simmer for 5 minutes, then stir in the cream. Season with salt and pepper and thicken with the cornflour dissolved in a little cold water.
Cook the pasta in boiling salted water according to the pack instructions.
Mix the drained pasta with the saffron sauce. Add the spinach, heat briefly and serve on plates with the smoked fish. Garnish with fresh chervil.