Preheat oven at 425°F (220°C).
In a large ovenproof skillet, melt butter and add flour. Whisk together to create a paste.
Add milk while stirring with the whisk. Let simmer until thickened.
Gradually mix in 2 cups (500 mL) of cheese to give it time to melt. Season with salt and pepper.
Add cooked macaroni, stir and warm up. Evenly spread out in skillet.
Top with pizza sauce, ham, mushrooms, peppers and the remaining cheese.
Bake in oven for 15 minutes, then broil for another 3 to 5 minutes. Let stand for 5 minutes before slicing pizza.