Add the onions and oil to a saucepan over low heat. Add sugar and cook, covered, for 30–35 minutes, stirring occasionally, until deep brown.

Add potato starch and stir over medium heat for three to five minutes.

Add the broth slowly, a bit at a time, stirring constantly.

Season with salt and pepper and continue to cook until the sauce reaches your desired consistency.

For a smooth sauce, blend the entire mixture with an immersion blender. For a chunky sauce, blend half the mixture and mix it with the remaining (unblended) sauce.