1 In a pot, bring salted water to a boil for the pasta. Cut the frozen salmon fillet with a sharp large knife into about 2 cm (approximately 3/4-inch) cubes.
2 Rinse endive, drain and thinly slice.
3 Rinse orange in hot water, wipe dry and finely grate the zest. Cut orange in half and squeeze.
4 Heat the oil in a deep skillet and cook the endive 1-2 minutes over medium heat.
5 Sprinkle flour over endive and pour in milk. Season with salt and pepper and add orange zest. Cover and cook over low heat for 5 minutes.
6 Cook pasta until al dente in the pot of boiling salted water according to package directions.
7 Add orange juice, sour cream and diced salmon to the endive. Simmer over low heat for 3-4 minutes. (If necessary, add a little water.) Season with salt and pepper.
8 Drain the pasta and serve with the salmon-endive sauce.