This makes a nice warm spreadable "jam" that is very oniony. A great uplift from raw onion slices or even simple buttered onions. Recipe began life on Simply Recipes, and was modified a bit from there.

Recipe below makes approximately 2 cups of jam.

Ingredients

2 sweet onions, medium dice
2 shallot
1/4 c scallion
1 teaspoons salt, plus more to taste
1/2 teaspoon olive oil
1 teaspoon ground black pepper
1 tablespoons fresh thyme leaves, divided
2 TBSP cup red wine vinegar
3 TBSP balsamic vinegar
1/2 cup- granulated sugar
1/2 lemon, zested (1 teaspoon) and juiced (1 tablespoon)

Directions

Salt the onions:
Place the diced onions in a medium bowl. Add 2 teaspoons of salt and mix well. Set aside at room temperature for 60 minutes. Do not strain the liquid from the onions, as it will help soften the onions as they cook.

Sauté and reduce onions:
In a 10-inch skillet over medium heat, warm the olive oil. Add the onions and their macerating liquid, and cook until translucent, stirring occasionally, about 10 minutes.

Add black pepper and 1/2 tablespoon of thyme leaves to the onions. Stir to combine. Reduce the temperature to medium-low and add the red wine vinegar and balsamic vinegar.

Cook for about 10 minutes, stirring occasionally. At this stage, the vinegars will have cooked down and into the onions. The mixture will have become thicker and heavier in the pan.

Reduce onion mixture:
Raise the temperature to medium-high, and add the sugar, lemon juice, and lemon zest, stirring to combine. The onions will darken considerably as the sugar takes on the color of the balsamic vinegar.

Add the scallions at this point.

Cook, for about 15 minutes or until you can pull a heat proof spatula through the onions leaving a path, and the mixture slowly comes back together. Stir occasionally, being careful the mixture doesn’t stick to the pan.

Season and cool:
Remove the pan from the heat. Taste first, then mix in the remaining 1/2 tablespoon of the thyme leaves IF NECESSARY, and allow the onion jam to cool in the pan. When fully cooled, season with salt, to taste.