In a medium bowl, whisk together the Dijon mustard and minced garlic until smooth.
Slowly drizzle in the olive oil while whisking continuously to create a smooth emulsion.
Add the balsamic vinegar, Worcestershire sauce, honey, rosemary, thyme, kosher salt, black pepper, and red pepper flakes. Whisk until fully combined.
Place the chicken in a large zip-top bag or shallow dish.
Pour the Balsamic Chicken Marinade over the chicken and turn to coat evenly.
Cover and refrigerate for 2 to 8 hours.
Choose your preferred cooking method:
Grill: Cook over medium-high heat for 4–5 minutes per side.
Bake: Roast at 425°F (220°C) for 18–25 minutes.
Pan-Sear: Cook in a lightly oiled skillet for 4–5 minutes per side.
Cook chicken until it reaches an internal temperature of 165°F (74°C) for breasts or 175°F (79°C) for thighs.
Let the chicken rest for 5 minutes before serving.
Garnish with fresh chives and enjoy.