Heat a large frying pan on medium heat with 2 tablespoon butter or olive oil as per your choice, on it and in the meantime season chicken breast with salt and pepper to taste.
Now add the chicken breast into the pan and cook it for 4 to 5 minutes until it becomes nicely cooked and golden brown. Follow this step for both sides
Now carefully transfer the chicken breasts into a bowl and wrap it with foil paper to keep it warm.
Place the same pan (do not clean the pan)on the heat and melt 2 tablespoon of butter. Now add the chopped onion and garlic and saute it for 1 minute until the onions become translucent. Stir it often to get a nice color of onions.
Now remove the pan from the hat and add white wine.
Return the pan to the heat and boil it for 3 minutes until it is reduced to half.
Add cream and stir it often for 3 minutes until the quantity is reduced by half.
Now sprinkle a good amount of chopped parsley on it. Add parmesan cheese over it and stir it gently.
Season it with salt and pepper. Be careful while adding these as you have already added salt and pepper to the chicken.
Add the spinach into the pan and simmer it until wilted. Now add the chopped mushroom into the sauce and stir it.
Place the golden sauteed chicken into sauce and coat the chicken properly with the sauce. If you want then you can also place the chicken on a serving plate and pour the sauce over it.
Now your Florentine Chicken is ready to serve. If you want then you can garnish it with more parmesan and a little bit of parsley.