Prepare the Chicken: Pat the chicken breasts dry using paper towels. Place them on a cutting board or plate and cover with plastic wrap. Use a meat mallet to pound the chicken until each piece is an even thickness—about ½ to ¾ inch—to ensure even cooking.
Season the Chicken: Sprinkle both sides of the chicken breasts with salt, pepper, garlic powder, and onion powder, ensuring they are evenly coated.
Sear the Chicken: Heat a large skillet or Dutch oven over medium heat. Add the olive oil. Once shimmering, place 2–3 pieces of chicken in the pan. Cook for 4–5 minutes per side, or until golden brown and the internal temperature reaches 165°F (74°C). Repeat with remaining chicken. Remove and set aside.
Deglaze the Pan: If your pan is coated with a thick layer of "fond" (browned bits stuck to the bottom of the pan after searing meat), I recommend deglazing the pan before moving to the next step. To do so, return the pan/pot to medium-high heat and add chicken broth or water (½ cup or more). As the liquid steams, scrape up the brown bits, adding more liquid as needed. Once all of the fond is removed, carefully pour the charcoal-looking liquid into a small bowl and set aside. Save it, don't discard.
Make the Roux: Melt the butter in the skillet and cook the garlic for 30 seconds.
Once the garlic is fragrant, whisk in the flour and dry ranch seasoning.
Whisk continuously for 1 minute to form a thick roux.
Make the Ranch Gravy: Slowly add the chicken broth AND the reserved fond liquid, whisking continuously until fully combined with the roux. Bring to a gentle simmer, then reduce the heat to low. Simmer for 2-3 minutes.
Add the Heavy Cream: Add the heavy cream and sour cream, whisking continuously until fully combined. Gently heat until thickened enough to coat the back of a spoon. Do not boil.
Return the Chicken to the Sauce: Turn off the heat and return the cooked chicken to the pan, nestling each piece into the creamy sauce. Cover with a lid and let it sit for 5 minutes to allow the flavors to meld and the chicken to soak up the sauce.