½cupred onion coarsely chopped (yellow onions also work but are less sweet)
¾cupbalsamic vinegar
1tbspunsalted butter.
1Tspsugar
Instructions
Coarsley chop the onion.
In a small saucepan, add the onions and 3/4 cup of balsamic vinegar and a 1 tsp of sugar. On a medium heat bring to a simmer and cook down on medium heat until the vinegar is almost gone (about 4-5 minutes). It will lose its acidity but still be tangy.
Remove from heat, blend in a cold tbsp of unsalted butter and set aside. As the balsamic cools down it will thicken further and if it gets too thick to pour as a sauce, stir in a teaspoon or two of water. Serve at room temperature.
Salt to taste and serve on any grilled meat or poultry or thick filets of fish.(See recipe notes below).