Quarter the onion half and roast the cut surfaces brown in a hot saucepan without oil. Cut the remaining vegetables into large pieces, add 2 tablespoons of oil to the saucepan with the onion and roast until they turn color. Now add the tomato paste and flour and roast for about 3 minutes. Deglaze with the red wine and let the liquid soak in.
Add the vegetable stock, bay leaf and allspice grains (it is best to hang them in a tea strainer) and simmer for 15 minutes.
Season to taste with salt and pepper, finely puree everything with a hand blender and pass through a sieve.
If the sauce is too thick, add a little more vegetable stock, if it is too thin, just let it reduce a little.