Season chicken with salt, pepper, and paprika (if using).
Heat olive oil and 1 tbsp butter in a large skillet over medium-high heat. Sear chicken until golden and cooked through, about 6–8 minutes. Remove and set aside.
In the same skillet, melt remaining 1 tbsp butter. Add onions and sauté for 2–3 minutes until soft. Stir in garlic and mushrooms; cook for 5–6 minutes until browned and tender.
Sprinkle flour over the mushrooms and stir well to coat. Cook for 1 minute.
Pour in chicken broth, scraping up any bits from the pan. Stir in Worcestershire sauce and Dijon mustard. Simmer for 3–4 minutes until slightly thickened.
Lower heat, then stir in sour cream and heavy cream. Mix until smooth and creamy.
Return chicken to the skillet, tossing to coat in the sauce. Simmer gently for 5 more minutes until heated through and sauce thickens to your liking.
Serve hot over egg noodles, rice, or mashed potatoes. Garnish with chopped parsley.
