Saute onion in olive oil. Once it softens add the flour and stir briskly. Stir until the flour develops a slightly brown color. This is the roux that will thicken our sauce while the potatoes bake. Spray a 9×13 pan with nonstick spray and layers the potatoes and ham. Pour chicken broth on top of the layers. Pour the roux on top of the potatoes and season with salt and pepper to taste. Cook for 30 minutes 350. Turn the temperature up to 400 and continue to cook another 15 minutes or until the top layer looks brown. Let sit 5 minutes and serve hot!