Fry the onions until translucent. Add the peas, sauté briefly. Deglaze with hot broth and simmer covered for about 10 minutes.
Remove about 1/4 of the peas with a slotted spoon. Finely puree the rest of the peas in the broth. Mix yogurt with sour cream, curry powder and flour until smooth, 4 tablespoon. put extra. Stir the rest of the yoghurt sour cream into the soup with a whisk, bring everything to a boil. Add the peas that have been retained. Season the soup with salt and pepper. Put a spoonful of yoghurt sour cream on each plate, top up with soup. Season cold milk with salt and pepper and froth up. Put on the soup and dust with curry powder.
If you like, you can of course add crayfish, prawns or the like.