Reduce fish stock with lemon grass by 1/3. Peel and finely dice the shallot. Heat the oil and fry the shallot until transparent. Sweat turmeric for a few seconds and stir in the fish stock. Add cream and simmer for 5 minutes.
Add cranberries and season with salt and pepper. Remove lemongrass.
Cook the spaghettini in plenty of salted water according to instructions al dente. Fillet the trout and cut into pieces. Mix the spaghettini with the sauce and serve with the trout fillet pieces and the trout caviar.
Serve sprinkled with chopped parsley.