Heat the oil in a large pot over medium heat. To test if the oil is hot enough, put a couple of kernels in the pot. When they start to pop or spin in the oil, it's ready.

Place popcorn kernels into the pot and give it a quick stir to coat them in oil. Place the lid on the pot, leaving a small gap for steam to escape. This helps keep the popcorn crisp.

Once the kernels start popping, gently shake the pot back and forth over the burner. This movement helps prevent the kernels at the bottom from burning and ensures even popping.

When the popping sound slows down to about 2 seconds between pops, remove the pot from the heat. Wait a few seconds to make sure there are no more pops. Then remove the lid and pour the popcorn into a very large bowl.

Combine the sugar and corn syrup in a small pot over medium heat. Cook, stirring occasionally, until it comes to a rolling boil. Remove the pot from the heat and mix in the peanut butter and vanilla.

Pour the peanut butter mixture over the popcorn and toss to coat. Store in an airtight container.