Cook the tortellini in plenty of boiling salted water for 15-16 minutes. Peel and finely dice onions. Coarsely chop the walnuts. Heat the fat, roast the walnuts in it and take them out. Sauté onion in frying fat until translucent.
Add flour and sweat while stirring. Deglaze with stock and cream, bring to the boil and simmer for about 5 minutes. Wash the chives and cut into fine rolls. Cut beef ham into strips.
Add 2/3 of the chives, walnuts and ham to the sauce and warm it up. Wash the lemon hot, halve it and squeeze the juice from 1 half. Season the sauce with lemon juice, salt and pepper to taste.
Arrange on a plate with the drained tortellini. Cut the remaining lemon half into slices. Serve the dish garnished with the lemon wedges and sprinkled with the remaining chives.