Cut each onion into 6 wedges. Sprinkle the chicken with pepper.
Coat a large nonstick frying pan with cooking spray or a little olive oil. Add 2 teaspoons butter and melt over a medium-high heat. Sauté the chicken for about 3 minutes on each side or until browned. Transfer to a plate.
Reduce the heat to medium, and melt the remaining butter in the pan. Sauté the onions with 1 tablespoon of the sugar for about 8 minutes or until they are golden brown and caramelised. Stir frequently, breaking the onions apart as they cook. Add the stock and boil for about 2 minutes or until it has evaporated.
Stir in the rosemary, thyme and remaining sugar. Return the chicken to the pan and sprinkle with the vinegar. Cook for a further 4 minutes or until the juices from the chicken run clear.
Some more ideas
*Use caramelised onions to top a homemade pizza, or stuff into pitta pockets along with fresh vegetables for a vegetarian sandwich. Or just serve as a side dish. *Replace the chicken breasts with boneless pork loin chops. *Does chopping onions make you cry? Blame it on the sulphuric compounds in the vegetable. One remedy is to leave the root end intact; this is where the compounds are concentrated. Or freeze the onion for 20 minutes before cutting, to inhibit the chemical release.
Caramelising the onions produces a rich flavour, and makes them much more palatable. The same cooking process can bring out the best flavour in other vegetables, such as carrots.