Slice the chicken breasts in half lengthwise to create 4 thinner pieces. Season with garlic powder, salt, and pepper.
Heat olive oil and 1 tablespoon of butter in a skillet over medium-high heat.
Once hot, add the chicken and cook for about 5-6 minutes per side until golden and fully cooked (165°F). Remove chicken and set aside.
Lower the heat to medium, add the remaining butter and sliced onion. Sauté until softened and lightly browned (about 10-15 minutes). Adjust heat as needed.
Add minced garlic and cook for 30 seconds.
Pour in chicken broth and Worcestershire sauce, scraping up any browned bits from the pan.
Mix in sour cream until smooth, heating gently for a couple of minutes without boiling.
Return the chicken to the skillet, spoon sauce over it, and season with additional salt and pepper if desired. Serve hot, garnished with chopped parsley.