Start by seasoning both sides of the chicken with salt and pepper.
Heat olive oil over medium-high heat in a big pan with sides. When its hot, sear the chicken on both sides till it is nicely browned and remove from the pan and set aside. It should take about 3 or 4 mins per side.
Add the onion to the pan and saute for a few mins. Add the garlic and 1 min later, add the wine to de-glaze the pan. Scrape up any bits of the chicken that have been stuck to the pan. Add the tomatoes to the pan and saute for a few mins.
Add the mustard and the chicken broth and give it a stir.
Finally, reduce the heat to medium and add the chicken back to the pan along with any juices that have pooled under the chicken as it has been resting. Cover and cook for 15 - 20 mins stirring the sauce around periodically. Check the chicken is done by cutting into it and making sure the parts by the bone are not pink anymore.
Once the chicken is done, season the sauce with salt and pepper to taste.
If your sauce seems to be evaporating too quickly or you want moresauce, just add a little wine or chicken broth as you are cooking.