In large pan, add oil and pop the corn according to instructions. Once popped, keep aside.
Now lay out two baking trays with parchment paper and keep aside. This is because as soon as the caramel popcorn is done it will need to be spread on a flat surface.
In a large saucepan, melt both the sugars until nice bubbling. The sugar should be a nice deep caramel shade. Add all the butter and cook for another two minutes until the sugar begins to smoke.
The longer you cook it the crunchier your popcorn will be. Add in the salt and then the baking soda. As soon as you add the soda, the caramel will bubble. Turn off the heat and stir well.
Pour in the caramel into the popcorn. Stir vigorously until most of the popcorn is coated with the caramel. Upturn the popcon onto the baking trays.
Bake for 45 minutes at 150 degree centigrade., turning it over at least once. Cool and serve