Prepare all the ingredients near your stove and place the pot lid on the side. Prepare a baking sheet lined with parchment paper.

Add the butter and vegetable oil to a 3-quart (2.8-liter) heavy duty deep pot. Heat over medium heat until the butter has melted. Add 3 to 4 popcorn kernels.

When the kernels pop, add the rest of the kernels. Sprinkle with sugar and chili flakes (if using). Swirl in the soy sauce and immediately cover the pot (*Footnote 2). Remove the pot from the stove and set a timer for 30 seconds. (*Footnote 3)

Turn to a medium-low heat. Put the pot back on the stove when the timer is up. Shake the pot a few times so the corns spread in an even layer. Once the kernels start to pop, shake the pot constantly to prevent the sugar sticking to the bottom and burning. Keep the lid slightly ajar to release the steam so the popcorn will be crispier (*Footnote 4). You should see a wisp of smoke coming from the gap. If you see too much smoke coming from the gap, remove the pot from the stove to let it cool off. Once the popping slows down, about a few seconds between pops, remove the pot from the heat. Uncover the pot and spread the popcorn onto the lined baking sheet. (*Footnote 5)

Now you can enjoy the popcorn while it is still warm!

The popcorn will stay crispy for 2 to 3 hours if your room is dry. For longer storage, wait until the popcorn cools down to transfer into a Ziplock bag and store at room temperature. Although it’s highly unlikely you’ll need to because the popcorn will be all gone really soon!