Pop the popcorn using your preferred method (air popper, stovetop, or microwave). Measure out 8 cups for caramel and 8 cups for cheese. Keep warm in a low oven (200°F) in two separate large bowls.
For caramel: In a medium saucepan over medium heat, melt the butter. Stir in brown sugar, corn syrup, and salt. Bring to a boil, stirring constantly. Boil for 4 minutes without stirring. Remove from heat and stir in baking soda and vanilla (mixture will foam).
Pour the caramel over one bowl of popcorn (8 cups) and stir quickly to coat. Spread on a parchment-lined baking sheet and bake at 250°F for 10 minutes, stirring once halfway. Let cool.
For cheese popcorn: Place the remaining 8 cups of popcorn in a large bowl. Sprinkle with cheddar cheese powder and toss until evenly coated. Add more powder to taste.
Combine the caramel and cheese popcorns in a large bowl or serve side by side. Enjoy immediately or store in an airtight container.
Tips
Use freshly popped popcorn for best texture; stale popcorn won't hold the coating as well.
Store in an airtight container at room temperature for up to 3 days.
For extra crunch, bake the caramel popcorn an additional 5 minutes.
Adjust the ratio of caramel to cheese popcorn to your preference.