1-Preheat the oven: Preheat the oven to 200°F (93°C) and line one or two 12×17-inch baking sheets with silicone mats or parchment paper.

2-Place the popcorn: Place the popcorn in a large bowl or spread it onto the prepared baking sheets.

3-In a medium saucepan: In a medium saucepan over medium heat, combine the brown sugar, light corn syrup, butter, salt, and cream of tartar. Stir constantly until the butter melts and the mixture begins to simmer. Allow it to bubble for 4 minutes without stirring, aiming for 234 235°F (112 113°C) if using a candy thermometer.

4-Remove from heat: Remove from heat and immediately stir in the baking soda, which will cause bubbling and frothing.

5-Pour the caramel: Pour the caramel over the popcorn and gently stir to coat evenly. Spread the coated popcorn evenly on the baking sheets if it isn’t already.

6-Bake: Bake for 1 hour, stirring every 20 minutes.

7-Allow the caramel corn to cool: Allow the caramel corn to cool on the pan for at least 30 minutes, letting the caramel harden as it cools. Break apart any large clusters once it is cool enough.

8-Store: Store in an airtight container for up to 2 weeks.