Place pounded chicken breasts in a shallow dish and pour buttermilk over them. Let marinate at room temperature for 15 minutes. Meanwhile, whisk together flour, garlic powder, paprika, 1/2 teaspoon salt, and black pepper in a wide shallow bowl. Remove chicken from buttermilk, letting excess drip off, then dredge in seasoned flour, pressing to adhere.

Heat vegetable oil in a large oven-safe skillet over medium-high heat until shimmering. Add chicken in batches if needed - do not crowd the pan. Cook 4-5 minutes per side until deep golden brown and internal temperature reaches 165°F. Transfer to a plate and tent with foil.

Pour off all but 2 tablespoons oil from the skillet. Reduce heat to medium and add butter. Once melted, add minced garlic and cook 30 seconds until fragrant - do not brown. Whisk in heavy cream and ranch seasoning. Simmer 3-4 minutes until slightly thickened. Taste and add remaining 1/2 teaspoon salt if needed.

Return chicken to the skillet, nestling into the sauce. Sprinkle remaining 3/4 cup Parmesan evenly over the top. Transfer skillet to broiler 4-6 inches from heat. Broil 2-3 minutes until cheese is melted, bubbling, and lightly browned in spots. Watch carefully to prevent burning.

Let rest 3 minutes before serving directly from the skillet. Spoon extra sauce over each portion.