For the meatballs, peel and finely dice the onion. Knead minced meat, onion, breadcrumbs, 2 tablespoons milk and mustard. Season well with salt, pepper and cayenne pepper. Shape into about 16 balls. Fry in hot oil all around for about 6 minutes.
For the asparagus stock, wash and peel the asparagus and cut off the woody ends. Boil the skin and ends in 1 l salted water with 1 tsp. sugar and lemon juice. Simmer for about 10 minutes. Drain, catch the stock and bring to the boil again.
Cut the asparagus spears into pieces. Cook the lower asparagus pieces (without heads) in the stock for about 5 minutes, add the asparagus tips for 3 minutes. Drain again and collect the stock.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Sweat flour in hot butter. Add 600 ml stock, wine, 200 ml milk and cream while stirring. Bring to the boil, simmer for about 5 minutes.
Season to taste with salt and sugar, heat asparagus in the soup, put meatballs on skewers and heat in a hot oven for about 5 minutes. Serve the soup with skewers.