Sprinkle the chicken with salt and pepper. Dredge the chicken in the flour to coat lightly then shake off any excess flour.
In a large skillet over medium heat, melt 2 tablespoons of butter.
Once melted, add the chicken and cook until brown, about 5 minutes per side.
Carefully move the chicken to a plate and cover with foil to keep it warm.
Melt 2 tablespoons of butter in the same skillet over medium heat. (Do not clean the skillet) Add the onions and garlic and saute until the onions are translucent, about 1 minute. Be sure to use a wooden spoon or spatula where you can be stirring and scraping the lovely brown bits that form.
Remove pan from stove and carefully pour in the wine.
Return pan to stove and increase the heat to medium-high and boil until the liquid is reduced by half, about 3 minutes.
Add the cream and boil until the sauce reduces by half, stirring often, about 3 minutes.
Sprinkle in the parsley.
Season the sauce with salt and pepper. (Be sure to try it as you go to determine the correct amounts!)
RETURN THE CHICKEN and any accumulated juices TO THE SAUCE (If you want you can turn the chicken to coat it in the sauce or you can pour it over when serving as I did. This will finish cooking the chicken) Turn heat to low/warming.
Meanwhile, melt the remaining 2 tablespoons of butter in another large skillet over medium heat. Add the spinach and saute until heated through.
Season the spinach with salt and pepper to taste.
Arrange the spinach over a platter. Place the chicken atop the spinach. Pour the sauce over and serve.