Prepare the pasta in salted water according to the instructions on the packet. Wash the tomato, rub dry, cut into quarters and cut out the seeds. Finely dice the flesh. Wash basil, dab dry and pluck leaves from the stalks. Peel onion and chop finely. Heat the fat in a pot and fry the onion until transparent. Dust with flour and sauté.
Deglaze with stock and cream while stirring. Season to taste with lemon juice, salt and pepper. Drain tuna, pluck into pieces and warm up in the sauce. Drain the pasta and let it drain. Mix the pasta carefully with the sauce. Garnish with diced tomatoes and basil