Heat oil in a saute pan over medium heat. Add onion and sugar and cook, stirring constantly, for 10 minutes, until mixture is syrupy. Add ginger and lemon juice.
Dissolve potato starch in orange juice and add to pot. Season with salt and pepper. Continue to cook until sauce thickens.
Recipe by Between Carpools at https://betweencarpools.com/5-things-make-for-pesach-using-duck-sauce/