Cook the pasta in boiling salted water according to the instructions on the packet. Meanwhile peel the onion, dice very finely. Wash basil, pluck leaves, chop larger ones. Melt butter, fry onion and crab meat in it.
Dust with flour and let it sweat on. Deglaze with white wine, stock and cream while stirring constantly, simmer for 2 minutes. Season to taste with salt and pepper, add basil. Arrange noodles and sauce in portions, garnished with basil.