In a heavy skillet slowly cook the diced pancetta in 1 Tbls of the oil until golden and crisp all over, about 10 minutes.
Remove the pancetta to a plate lined with paper towels, leaving the fat behind. Add the other Tbl of oil to pan along with the sprouts and diced onions. Brown the sprouts over med heat. Try to heat sprouts in a single layer. When sprouts are lightly browned add the chicken broth and water, cover immediately. Simmer until the sprouts are fork done. Remove sprouts from pan and let them hang out with the waiting pancetta. Return the pan to medium-high heat, Now add the balsamic vinegar and a bit of pepper to taste, let this low boil for about 5 mins. Add the butter, when melted add back your sprouts and onions. Toss to coat and heat through. Top with Pancetta and serve.