Melt the butter in a large saucepan over medium heat and sauté the onions in it.
Dust the flour over it and brown it lightly. Slowly add water, stirring constantly, until a thick mass is formed.
Stir in milk. Now you must have made a creamy soup. Add herbs (e.g. garlic mustard, parsley, chives ), the oil / bacon (roasted or not depending on your taste) and / or mushrooms (chanterelles, mushrooms ) and let it steep a little.
Season with salt, pepper and nutmeg.
Simple, inexpensive and delicious - wonderfully warm on cold evenings in the warehouse.
It tastes twice as good when warmed up - if something is left over.