Preheat oven to 350 degrees. Grease a 5-quart (11 x 15) casserole dish and set aside.
Heat 2 tablespoons corn oil in a large skillet over medium-high heat.
Mix in onion, carrots, and celery.
If using raw ground turkey, add it to the skillet, too.
Season with salt, pepper, and cayenne.
Let cook, stirring occasionally, until onions are soft and meat is browned, about 8 minutes.
Meanwhile, heat 1/4 cup corn oil in a large sauce pan over medium heat.
Pour in flour and stir until browned, about 1 minute.
Slowly whisk in milk. Cook, stirring occasionally, until thickened. About 6 minutes.
Mix 1 1/2 cups cheese into milk sauce and turn off heat.
Add cooked vegetables, turkey, cooked pasta, sour cream and chopped broccoli to pot of sauce. Gently stir.
Spread casserole mixture into greased casserole dish.
Sprinkle with remaining 1/2 cup cheese.
Bake, covered, for 25 minutes. Remove cover from casserole dish and bake an additional 5 minutes.
Remove from oven and serve hot.