Season chicken thighs with salt, pepper, coriander, and mustard covering both sides and all areas.
Heat 12” skillet over medium-high heat. Add oil and swirl to coat pan. Arrange chicken in a single layer and cook thoroughly getting a nice sear on both sides, about ten minutes total. Transfer the chicken to a plate and cover with tin foil.
In the same skillet over medium-high heat add the chicken stock and deglaze the pan by scraping up bits from the pan using a rubber spatula or wooden spoon. Next, add in the crème Fraiche and mix well. Let reduce down by half while stirring often, roughly 5-10 minutes.
Add in the lemon juice, tarragon, and chives then immediately pour the sauce over the chicken to serve.