Dredge each chicken breast in a bowl of flour. Season each side of the chicken breasts with salt, pepper, garlic powder, and smoked paprika. Set aside.
Add 1 tablespoon of butter and 1 tablespoon of olive oil to a large skillet, and heat over medium-high heat.
Add the chicken to the hot skillet and sear for approximately 4 minutes.
Flip and sear for another 4-5 minutes, until lightly browned. Transfer the chicken to a clean plate and set aside.
Melt the remaining 2 tablespoons of butter in the hot skillet. Add the onions and sauté until translucent. Add the garlic and sauté until fragrant, about 1 minute.
Add the sliced mushrooms, Dijon mustard, and flour. Stir and cook for 3 minutes coating the mushrooms in Dijon and flour.
Pour in the beef broth, chicken broth, Worcestershire sauce, and black pepper. Scrape any brown bits off the bottom of the skillet. Cook, stirring occasionally, until the sauce begins to thicken, about 4 minutes.
Reduce heat to medium-low and stir in the sour cream. Continue to whisk the sour cream into the sauce until it becomes smooth, about 5 minutes.
Return chicken breasts to the skillet. Simmer until the chicken is cooked through.
Serve over egg noodles and garnish with fresh parsley.