Remove chicken from packaging, pat dry, and season with salt, herb de Provence and black pepper. Let sit at room temperature for 30–45 minutes before searing. While the chicken is resting, prep onion, leeks, and garlic.
Preheat oven to 375 degrees
Heat Cast Iron (preferably) or another oven-safe skillet over medium high heat. Add about 1 tbsp of olive oil. Sear chicken, skin side down, working in batches. Sear until skin golden brown, remove from pan and set aside. Repeat.
Turn heat down to medium and melt butter in the skillet and sauté onions, leeks, and garlic until just translucent but not brown, about 5–7 minutes.
Deglaze pan with white wine, chicken stock, and lemon juice. Add fresh tarragon. Let gently simmer 5-10 minutes.
Remove from heat, return the seared chicken to the skillet, skin side up, and transfer to the oven to bake for 25–35 minutes or until a meat thermometer reaches 165 degrees F.