Pop microwave popcorn according to manufacturers instructions, then set aside in a large bowl.
If you don't use microwave popcorn, I suggest also buttering ( with 1/4-1/2 cup of butter) and salting your home popped popcorn for added flavor. You can adjust the amount of salt to your personal preference.
In a medium saucepan, completely melt butter 1/2 cup (1 stick) of salted butter, over low to medium heat.
(Do not use high heat as you will make toffee instead of caramel.)
Stir in 1/2 cup brown sugar to the melted butter, continue to stir until fully combined and slightly bubbling.
Add 10-12 marshmallows into the caramel mixture, stir vigorously until fully incorporated and smooth.
Carefully pour warm caramel sauce over popped popcorn in the large bowl, stir to combine for the perfect texture and coating of smooth, soft caramel.
Alternatively, you can spread the popped popcorn onto a parchment paper lined baking sheet/ cookie sheet and pour the caramel sauce over the spread out popcorn. Serve and enjoy! Try not to eat the whole thing on your own, or do it anyway. I really won't judge. :)
For storage or keeping any leftover homemade caramel corn, place it into an airtight container or food safe storage bag. Remove as much air as possible before closing.