Cut the sausages into slices, peel and quarter the onions. Fry both in hot fat, then remove. Dust the flour into the fat and brown while stirring. Deglaze with the milk, bring to the boil and stir in the mustard. Season to taste with salt and pepper, possibly add granular broth to taste.
Add the sausage and onions again. Sprinkle with chives and serve with potatoes, rice or baguette.
Can be extended with various vegetables as desired.