Peel and finely chop the onion. Mix minced meat, egg, onion, breadcrumbs and mustard. Season with salt and pepper and form small balls. Heat the oil in a large pan. Fry the meatballs all around until golden brown.
Add frozen vegetables. Deglaze with broth and simmer for about 8 minutes. Season to taste with salt and pepper. Stir in cream for refinement. Serve garnished with parsley