1. Preheat oven to 300°F. Line a large baking sheet with parchment paper or a silicone mat. Use a rimmed baking sheet so the popcorn stays contained while you bake and stir.

2. Pop the popcorn kernels using an air popper into a large bowl. Measure 1/2 cup unpopped popcorn kernels to yield about 16 cups popped popcorn. If you do not have an air popper, microwave plain kernels in a paper bag or use a stovetop pop method; just avoid pre-buttered microwave bags because added oil can make the caramel slide off.

3. In a small saucepan, melt 1 cup salted butter, 1 cup light brown sugar, 1/3 cup light corn syrup, and 1 teaspoon of the kosher or sea salt over medium heat. Stir until everything is incorporated and begins to simmer. The butter melts first, then the sugar dissolves into a syrupy mixture.

4. Bring to a boil and continue boiling for 4 minutes without stirring. Use a timer and moderate heat so the sugar cooks evenly. Boiling without stirring helps the caramel develop without seizing. If you are making a vegan version, use plant-based butter and follow the same timing; the visual cues are the same.

5. Remove from heat and let cool for 2 minutes before pouring over popcorn. This brief cooling prevents the caramel from being so hot that it immediately pools off the popcorn.

6. Pour the caramel mixture over the popcorn and stir to coat evenly. Work quickly but gently: a large, heatproof spatula or wooden spoon helps fold the popcorn so kernels don’t break. Make sure to get into corners of the bowl so every piece gets a light coating.

7. Spread popcorn on the prepared baking sheet, sprinkle the remaining salt (between 1/2 and 1 teaspoon to taste), and bake for 30 minutes, stirring every 10 minutes. Move the popcorn gently while baking: stirring prevents pools of caramel and keeps the coating uniform. Set a timer for each 10-minute interval to avoid burning.

8. Allow the caramel popcorn to cool on the counter before serving. Cooling lets the caramel set and crisp up. Once cooled, break into clusters or store in an airtight container.