For the lentil stew, strain the lentils and collect the liquid from the can. Heat the oil and fry the finely chopped onion in it.
The onion can take some color (good for the taste), but should turn yellow at most, not brown. Then add the flour and stir well.
Let the roux fry for a minute or two and then deglaze with a small shot of vinegar. Then add the liquid from the can, crumble in the vegetable soup cube and bring everything to a boil while stirring.
The sauce should boil for a few minutes so that it reduces a bit and so that the flour taste goes away. When the sauce has reduced to a creamy consistency, add the lentils and cook for 1 – 2 minutes.
Season to taste with salt, pepper and thyme (preferably fresh, otherwise from a jar).
The lentil stew tastes very good with bread dumplings or also with sausages and fresh bread, also noodles go well with it.