Melt the butter in the same skillet over medium to medium-low heat. Use a spatula to scrape the bottom of the pan, releasing any flavorful bits left from the chicken.
Add the garlic cloves and cook for 6–7 minutes, stirring occasionally, until softened and slightly caramelized.
Stir in the flour and cook for 1–2 minutes, until the raw flour smell disappears.
Gradually add the chicken broth mixture, stirring constantly to avoid lumps.
Mix in the heavy cream and bring the sauce to a gentle boil. Reduce heat to low and stir in Parmesan cheese, if using.
Return the chicken to the skillet along with any juices. Spoon the sauce over the top, cover partially, and simmer for 5 minutes until heated through.