Peel and wash the potatoes and cook them in boiling salted water for about 20 minutes. In the meantime, clean, wash and quarter the fennel. Cut out the stalks, chop the fennel greens. Fennel quarters in boiling broth, seasoned with lemon juice, cook for 12-15 minutes.
Clean, wash and halve the tomatoes. For the sauce, melt the fat and sweat the flour in it. Add 1/8 litre fennel stock, cream and milk while stirring constantly, bring to the boil. Stir in cheese. Season to taste with salt and pepper.
Warm up the tomatoes in it. Wash the chives, cut into small rolls except for a few tips for garnishing. Drain the potatoes. Arrange vegetables, potatoes and sauce on plates, sprinkled with fennel greenery and chives.