Season chicken with salt, pepper and garlic powder.
Heat oil in a large skillet over medium-high heat. Add chicken and brown on all sides, about 3-5 minutes. You might need to do this in batches so you don't crowd the pan. Once the chicken is browned, remove to a plate.
Add vinegar and let cook off, about 1 minute. Be careful not to inhale that vinegar-it will clean your sinuses out!
Add butter, onions and rosemary to pan. Cook until the onions are soft, about 4-5 minutes. Add the garlic and stir.
Add flour to pan and stir to combine and let cook for about 1 minute, just until the flour is no longer "raw".
Whisk in the wine and let reduce slightly. Whisk in broth and let come to a slow simmer. Add the chicken back to the pan and let finish cooking. If you use small cubes of chicken this should only take about 3-5 minutes. If you prefer whole chicken breasts let the chicken cook in the sauce for about 10-12 minutes or until completely cooked through.
Notes:
* I use beef broth because it gives it a richer taste, but if you only have chicken broth it will work just as well.
* You can use chicken thighs, chicken breasts, pork chops....
* I serve this over noodles or rice, but you can serve it plain with a steam vegetable.