Preheat the oven to 375°
Rub a 9x13 inch baking pan or oven-safe dish with butter
Bring a medium pot of water to a boil and add the olive oil to it
Add the macaroni and cook until al dente, about 4-5 minutes, drain and set aside
In a large pan met the butter until frothy and then add the flour
Whisk until a paste is formed then add. about ¼ cup of milk
Whisk until smooth and repeat until almost all of the milk has been added
Turn the heat up to medium and bring to a light simmer
Cook for about 3-4 minutes then add the grated cheddars whisking them into the sauce until smooth.
If the sauce seems to thick just add some extra milk and whisk
Place the elbow macaroni into the 9 x13 pan
Add the chopped chicken, ham and peas and stir
Pour the cheese sauce over the pasta and mix well
Bake in the oven uncovered or about 20-25 minutes and bubbly around the edges
Let it rest for 5 minutes and then serve in bowls garnished with chives or parsley if desired