Cook the spiral noodles in 3 1/2 l boiling salted water according to package instructions until al dente. Meanwhile, wash the tomatoes and cut into small cubes, removing the stalks.
Wash the basil and shake dry, pluck the leaves and chop finely. Rinse the pasta in cold water and drain well. Mix the egg yolks well with the mustard and lemon juice. Whisk the oil into the egg yolks, first drop by drop, then in a thin stream.
Mix in the sour cream. Season the mayonnaise with salt and pepper. Mix the pasta with the tomatoes and basil. Fold in the mayonnaise and season the salad if necessary.