How to Make It
Melt the butter in a medium skillet. Add the onions and cook over moderate heat, stirring, until soft and just translucent, about 8 minutes. Add the sugar, wine, vinegar, grenadine and a pinch of salt. Cook over low heat, stirring, until the liquid thickens and coats the back of a spoon, about 35 minutes. Transfer the onion jam to a bowl and let cool.