In a large, deep pan, heat the oil and pop 6 quarts of popcorn. Spread the popcorn on two baking sheets, leaving any unpopped kernals behind.
In a medium saucepan, combine the brown sugar, corn syrup, butter, cream of tartar and salt. Bring to a boil over medium-high heat and cook for 5 minutes, stirring constantly.
Remove from heat and add the baking soda; the mixture will puff up as the baking soda is stirred into it. Pour the caramel evenly over the popped corn and immediately mix thoroughly with a large metal spoon or plastic spatula.This is more of a folding motion than stirring to coat the popcorn with the caramel.
Place both pans in the oven on middle shelves and bake for 1 hour (this is what crisps up the caramel corn), rotating the pans to opposite shelves half way through the baking time and turning the caramel corn over with a spatula every 20 minutes for even baking.
Immediately turn the caramel corn out onto sheets of waxed paper and when cool enough to handle, break into pieces. Serve immediately.