The reduced balsamic vinegar sauce gives the flank steak a unique flavor that pairs perfectly with the caramelized onions. Both the steak and onions contribute a hefty dose of potassium to this entrée--766 milligrams in each serving. Serve with steamed broccoli or asparagus, and drizzle some of the glaze over the vegetable.
Bring balsamic vinegar to a boil in a small, heavy saucepan. Reduce heat to medium; cook until reduced to 1/4 cup (about 5 minutes). Remove from heat.
Heat oil in a large nonstick skillet over medium-high heat. Add onion, and sauté 10 minutes or until tender. Sprinkle with 1/4 teaspoon salt; sauté 18 minutes or until onions are golden brown. Remove from heat.
Sprinkle steak with remaining 1/4 teaspoon salt, pepper, and thyme. Place steak on a broiler pan coated with cooking spray; broil 6 minutes on each side or until desired degree of doneness. Cutsteak diagonally across grain into thin slices. Serve steak over onions; drizzle with balsamic glaze.
Wine note: Steak and caramelized onions are fabulous partners for numerous red wines. But the balsamic vinegar glaze presents a bit of a challenge since vinegar can make wine taste sharp. One variety stands up especially well to vinegar: syrah (also known as shiraz). There are many great syrah/shirazes available. Try Geyser Peak Winery's shiraz from California, which is dense and lipsmacking--a steal at $ -Karen MacNeil
I made this for the first time for myself and a guest. I did this after work and just didn't allow enough time. That is not my only mistake but, before I elaborate more about my foolishness, let's talk about the recipe. I cooked the steak according to the directions (a little longer than the recipe called for actually), but it was too rare for my guest. It would have been very helpful if the recipe said... 1 inch steak rare - 6 minutes; medium rare... The onion preparation instructions were easy to follow, though because I was short on time, I just got them to the tender point (not browned), and the balsamic reduction was a cinch. I got it to a slow rolling boil and let it go for about 5 minutes or so... swished it around and watched the liquid. It seemed thicker. Great. Poured it into your serving dish. OK, back to my foolishness: To remove some of the pinkness, I put the sliced steak in the micro. This made it tough & changed the aroma to something not great. Beginner's mistake :(
Followed the recipe exactly as written and it turned out great. The combination of the onions and balsamic glaze is great together. Quick enough to make for two, but would definitely make for company. Will make again!