Combine garlic powder, onion powder, paprika, salt, and pepper in a small bowl. Pat chicken breasts dry with paper towels and season both sides with spice mixture. Set aside.
Melt 1 tablespoon butter in a large nonstick skillet over medium heat, and add olive oil. When the butter stops sizzling, add onions and cook, stirring occasionally, until tender, about 5 minutes. Remove to a plate and keep warm.
To the same skillet, add remaining butter. Increase heat to medium-high. When butter is melted, add seasoned chicken breasts to the skillet and cook until lightly browned, about 3 minutes. Turn chicken, and return onions to the skillet, placing around and on top of chicken. Stir in minced garlic and cook about 30 seconds, or until fragrant.
Dissolve chicken bouillon cube in hot water; add to the skillet with white wine, Worcestershire sauce, and Dijon mustard. Bring to a boil, cover, and reduce heat to medium-low. Cook, undisturbed, until chicken is no longer pink at the center, 10 to 15 minutes; an instant-read thermometer inserted near the center should read at least 165 degrees F (74 degrees C).
Remove skillet from heat and stir in sour cream, making sure all the onions are incorporated.
Garnish with fresh snipped parsley and parsley sprigs. Serve immediately.
