Place cubed potatoes into a large pot of water and bring to a boil. Cook until tender when pierced with a fork, then drain and return to the pot. Stir in half and half, butter, and sour cream, seasoning to taste with salt and pepper. Mash using a masher or mixer until smooth and creamy, then cover to keep warm.

Meanwhile, slice chicken breasts crosswise for quicker cooking. Generously season both sides with salt, pepper, garlic powder, and onion powder.

Heat olive oil in a skillet or cast iron pan over medium-high heat. Once shimmering, add chicken and sear for 3–4 minutes per side, until golden and cooked through. Remove chicken to a plate and tent with foil.

In the same pan, melt butter over medium heat. Whisk in flour and cook for one minute. Gradually pour in the chicken broth, followed by chicken bullion, cream, garlic powder, onion powder, and Worcestershire sauce. Stir and simmer for 2–3 minutes, allowing the sauce to thicken and deglazing the pan in the process.

Incorporate Parmesan cheese into the sauce. Return the chicken and its juices to the skillet, spooning the sauce over the pieces and warming them through.

Plate the mashed potatoes and top with the chicken, ladling generous amounts of the sauce over the top before serving.