For the sauce, peel and finely dice the onion. Heat oil, fry onion until translucent, dust with flour, sauté briefly. Add stock, milk and cream while stirring, bring to the boil and simmer for about 10 minutes, stirring occasionally.
Roughly dice the cheese, add to the sauce and dissolve while stirring. Season to taste with salt, sugar and pepper. Wash and halve the tomatoes. Wash basil, shake dry, pluck leaves from the stalks and chop.
Clean, wash, shake dry and, depending on the size, cut into small pieces if necessary. Finely slice Parmesan cheese. Add basil and tomatoes to the sauce and warm up slowly. Meanwhile prepare pasta in boiling salted water according to the instructions on the packet.
Mix pasta, sauce and rocket and arrange in a large bowl. Sprinkle with parmesan.