Cheesy Ham and Pasta Bake

I found this recipe via orgjunkie from the Finding Joy in My Kitchen blog.

1 lb. whole wheat penne pasta (I used regular penne)
2 C extra sharp cheddar cheese (I used medium cheddar)
1 1/2 C diced ham
8oz. mushrooms, sliced (My small hometown grocery store only had large mushrooms for $3.99; I used canned instead, although fresh would definitely be better)
I also added some frozen peas
4 T white wheat flour
3 C milk* (divided) (I ended up using about 2 cups)
1/4 tsp. pepper

Begin by boiling the pasta according to package directions. Then, mix together 1 C milk and flour in a large measuring cup. Meanwhile, saute the mushrooms in a large skillet with a little olive oil, if necessary. When mushrooms are cooked, remove from the pan and toss with diced ham.
In the same skillet, pour the milk mixture into the pan. Stir constantly, adding additional milk to reach desired thickness while warming the mixture so that it thickens. Simmer about 3 minutes.
Add in the ham and mushroom mix, and simmer until ham warms. Then, add in 3/4 of the shredded cheese.
Spread the pasta into a 9x13 glass baking dish. Pour the cheesy sauce over the pasta. Stir to coat. Then, sprinkle with remaining cheese. Stick the dish into a warm oven... about 300 degrees, for 10 minutes, until the cheese on the top melts.