Place a large pot of water on the stove-top to boil. Keep this water on high heat.
Wash and peel the sweet potatoes. Cut them up into small pieces and place them in the boiling water.
After 6-7 minutes of the potatoes boiling, add in the pasta.
After another 6-7 minutes, add in the corn and mushrooms. Boil for one more minute and then remove from the oven and drain. Pour this mixture into an 8 x 8 baking dish.
Meanwhile, in a large sauce pan over medium heat, combine two cans of cream of mushroom soup, milk, and sour cream. Add in salt and pepper and stir well. Keep on medium heat for about 2 minutes.
Lower the heat and let simmer until the pasta and sweet potato mixture has been drained.
Pour the mushroom cream sauce over the pasta and sweet potato mixture in the 8 x 8 dish.
*Both the sauce and the pasta mixture should finish up about the same time and should be hot and ready to eat. If this isn't the case, warm up the casserole (covered with foil) in a 350 degree F oven for about 10 minutes or until warmed through.
If you want to make this casserole beforehand, make it according to the instructions and then cover with foil and leave in the fridge. When you are ready to cook it, cook the covered casserole in a 350 degree F oven for 20-25 minutes or until warmed through.