Halve the king prawns and toss in flour, pepper and salt (little, as the mussels are already quite salty). Finely chop the onions, garlic cloves and parsley.
Heat the olive oil. Fry the onions, garlic, parsley, mussels and king prawns in the hot olive oil until the onions turn golden yellow. Deglaze with white wine and continue to simmer. When the white wine has reduced, add the broth and reduce the temperature a little. Simmer until the mussels are cooked through.
Then add the creme fraiche and nutmeg, stir in and, if necessary, season again with pepper, nutmeg and salt (unlikely). Cook the spaghetti to the desired firmness - recommendation: al dente. Pour into the sauce and serve immediately on preheated plates.