Remember to remove any up-popped popcorn kernels. *Popcorn can be air-popped to reduce fat or popped in oil, (your choice) *If popped in oil, place the popped popcorn in a paper bag to help drain excess oil.
Preheat oven to 250 degrees. Place popped popcorn in a large roasting pan sprayed with non-stick cooking spray. Set aside.
In a small bowl, mix together the salt, cheddar cheese powder, mustard powder, and chili powder. Set aside.
In a small saucepan, melt butter over low heat until melted or in a microwave safe glass bowl, microwave butter on low until melted. Pour the melted butter over the popcorn in roasting pan. Shake or stir to coat evenly. Immediately pour the cheese mixture over the buttered popcorn. Shake or stir to coat evenly.
Place roasting pan in pre-heated oven. Bake 20 to 30 minutes, stirring every 10 minutes.
Remove from oven, mix together with caramel corn for Chicago-style popcorn.
Store in airtight containers or ziplock storage bags.