01 - Pat the chicken breasts dry with paper towels and season both sides generously with salt and freshly ground black pepper.
02 - Heat olive oil in a large skillet over medium-high heat. Add the chicken breasts and sear until golden brown, about 4 minutes per side. Remove the chicken from the pan and set aside on a plate.
03 - In the same skillet, add the finely chopped onion and cook until softened, about 3 minutes. Stir in the minced garlic and cook for 1 additional minute until fragrant.
04 - Reduce heat to medium. Stir in the Dijon and wholegrain mustards, mixing thoroughly with the onion and garlic until well combined.
05 - Pour in the chicken stock and bring to a gentle simmer, scraping up any browned bits from the bottom of the pan to incorporate into the sauce.
06 - Stir in the heavy cream and honey until the sauce is smooth and homogeneous. Return the seared chicken breasts to the skillet, spooning the sauce over the top.
07 - Simmer uncovered for 15 to 20 minutes, or until the chicken is cooked through to an internal temperature of 165°F and the sauce has thickened to a creamy consistency.
08 - Stir in the chopped tarragon, adjust seasoning with salt and pepper to taste, and garnish with fresh parsley before serving.