Start by seasoning the chicken breasts with salt and black pepper on both sides.
In a large skillet, heat the olive oil and butter over medium-high heat until the butter is melted and bubbling.
Add the chicken breasts to the skillet and cook for about 5-7 minutes on each side, or until they are golden brown and cooked through (internal temperature should reach 165°F). Remove the chicken from the skillet and set aside on a plate.
Carefully add the brandy or cognac to the skillet, scraping up any browned bits from the bottom. Allow it to simmer for about 1-2 minutes to reduce slightly.
Stir in the heavy cream, Dijon mustard, and Worcestershire sauce. Cook for an additional 3-5 minutes, stirring frequently, until the sauce thickens.
Return the chicken to the skillet, spooning the sauce over the top. Cook for another minute to heat through.
Serve the chicken hot, garnished with chopped parsley.