A classic way to do many vegetables but especially nice with onions. I am reminded because I made them yesterday to serve with short ribs braised in coffee/ancho chile sauce. Cippoline are the small, very flat 1-2" round onions just now in our markets.
1 # cippoline peeled, root end intact. Cook 20 min in water and 1 1/2 T butter in a pan in which the onions sit flat with the water almost up to the tops. Turn once or twice.
Add slightly less than 1T. vinegar - I use a good wine vinegar. If you use balsamic, use less sugar, pinch of salt and slightly less than 1 tsp sugar.
Cook at a bare simmer for 2 hrs. You want to end up with a rich, brown
syrup. If too dry before finished add a bit of water.
Mamma Mia !