Peel and wash the potatoes and cook them in salted water for 15-20 minutes. In the meantime peel and wash the carrots and kohlrabi and cut them into small pieces. Wash the asparagus, cut off the woody ends briefly. Cut asparagus into bite-sized pieces. Boil 600 ml salted water. Cook carrots and kohlrabi for about 12 minutes, asparagus for about 7 minutes. Drain the vegetables, keep the stock.
Melt the fat. Peel and finely dice the onion and sauté in it. Add flour and sauté. Add white wine, vegetable stock and cream while stirring constantly, bring to the boil. Let carrots, kohlrabi, asparagus and peas simmer for about 5 minutes. Cut off chervil leaves and stir in. Season to taste with salt, pepper, nutmeg and a few drops of lemon juice