01 - Pat chicken breasts dry with paper towels. Season both sides generously with kosher salt and freshly ground black pepper.
02 - Heat olive oil and butter in a large skillet over medium-high heat. Add chicken breasts and sear for 4–5 minutes per side until golden brown. Remove chicken from skillet and set aside on a plate.
03 - Reduce heat to medium. Add chopped shallots and minced garlic to the skillet. Sauté for 2–3 minutes until softened and fragrant, stirring occasionally.
04 - Stir in Dijon mustard and whole-grain mustard until combined. Pour in dry white wine, scraping up any browned bits from the bottom of the pan. Let simmer for 2 minutes to reduce slightly.
05 - Pour in chicken stock and bring to a gentle simmer. Stir in heavy cream and fresh thyme leaves. Let the sauce cook for 1–2 minutes until slightly thickened.
06 - Return chicken breasts to the skillet, nestling them into the sauce. Cover and cook for 10–12 minutes until chicken is cooked through (internal temperature reaches 165°F) and sauce has thickened.
07 - Taste the sauce and adjust seasoning with additional salt and pepper if needed. Transfer chicken to serving plates and spoon sauce generously over the top. Garnish with chopped fresh parsley.