Melt fat in a saucepan over medium heat.

Add flour and finely chopped onions to the melted fat.

Cook, stirring frequently, until the onions are pale yellow, about 5-7 minutes.

Gradually add cold stock, stirring constantly to prevent lumps from forming.

Stir in caraway seed.

Bring the sauce to a boil, then reduce heat to low.

Simmer gently for 10 minutes, stirring occasionally, until the sauce has thickened.

Mash any remaining large onion pieces with a spoon or potato masher for a smoother consistency.

Season with salt to taste.

If desired, add vinegar and sugar to balance the flavors (a pinch of sugar and a splash of vinegar are recommended).

Serve hot.