Peel the onions and cut / chop into coarse strips. Melt the butter or clarified butter in a suitable saucepan and brown the bacon in it or fry it until crispy (depending on your taste, crispy = spicy!). Add onions and sauté until translucent. Add the chopped tomatoes and white beans with liquid, bring to the boil briefly and gradually deglaze with the stock until a good, stew-like consistency is obtained (should not be too thin, but also not too thick).
Let the stew just simmer on low heat for about 10-15 minutes. Season with salt, pepper and, if you like, with cayenne pepper and / or chilli flakes. Refine with parsley and, if necessary, with cream or homemade kefir.
Excellent fresh Black Forest farmhouse bread and baguette go well with it.