Put oil and butter in a large heavy bottom pot over medium heat until oil is heated and butter is melted.
Add popcorn and cover with a lid, leaving an opening for steam. I use an oversized lid so the steam can escape, but the pot is covered.
As the kernels begin to pop shake the pan slightly. When the popping slows down, remove from heat. I let mine sit for a bit in case there are any kernels that are still popping.
I pour a third of the popcorn into the bowl, salt to taste, and then repeat with the remaining popcorn.