This onion sauce is the authentic sauce to go with Kalbsbratwurst. But it is also excellent with all sorts of other sausages (Cumberland, for example), and with beef, mutton, and veal.

It’s thickened by using a roux – cooked flour and butter.

Recipe for an authentic onion sauce

Serves 4

Ingredients

• 2 onions
• 1 tbsp flour
• 2 tbsps butter
• 1 tsp mustard
• 1 tsp tomato paste
• 120ml/½ cup red vermouth
• 240 ml/1 cup beef stock (made with water and a couple of beef stock cubes, or ideally buy real)

Method

1. In a small saucepan melt 1 tbsp butter.
2. Peel and chop the onions and gently fry until they turn transparent.
3. Add a second tbsp of butter, and melt. Add the flour, mix well and cook gently for about ten minutes – you are making a roux.
4. Add the mustard and tomato paste. Mix in well.
5. Slowly at the vermouth and stock – very slowly at the beginning, adding just a little at a time and mixing the pasty onion mix in well to avoid lumps.
6. Simmer about twenty minutes, until the sauce is thick, unctuous and reduced to about two-thirds of its previous volume.