For the chicken, pound it with a mallet before cooking. When pounding, make sure to place a plastic wrap on top of the chicken to prevent it from tearing off.
Season one side with a bit of salt and pepper. Set it aside in a rectangular baking dish.
For the sauce, melt butter in the heated pan.
After, sauté onion leeks and all-purpose flour. Lower down the heat to prevent the flour from burning.
Add salt and ground pepper. Pour over the milk.
Use a whisk to mix all the ingredients together to avoid lumps in the sauce. Let it simmer.
When sauce is thick enough, add spinach and chopped ham.
When the sauce is done, pour it over the seasoned chicken.
Top it off with grated cheese.
Bake it in 350 degree F.