Instructions

1. Remove and reserve chicken tenders (if attached) for another use. Slice each breast in half horizontally to make 4 pieces total. Place on a cutting board and cover with a large piece of plastic wrap. Pound with the smooth side of a meat mallet or a heavy saucepan to an even thickness of about ¼ inch.
2. Sprinkle with ¼ tsp each salt and pepper. Place flour in a shallow dish and dredge the cutlets to coat both sides, shaking off excess. Discard remaining flour.
3. Heat 2 Tbsp oil in a large skillet over medium-high heat. Add 2 pieces of chicken and cook, turning once, until evenly browned and cooked through, 2 to 3 minutes per side. Transfer to a large serving plate and tent with foil to keep warm. Repeat with the remaining chicken.
4. Add the remaining 1 Tbsp oil, tomatoes and shallot to the pan. Cook, stirring occasionally, until softened, 1 to 2 minutes. Add vinegar; bring to a boil. Cook, scraping up any browned bits from the bottom of the pan, until the vinegar is reduced by about half, about 45 seconds.
5. Add broth, garlic, fennel seeds and the remaining ¼ tsp salt and pepper. Cook, stirring, until the sauce is reduced by about half, 4 to 7 minutes.
6. Remove from heat; stir in butter. Serve the sauce over the chicken.