Preheat the oven to 350°F/180°C (160°C fan oven), and line 3 cookie sheets with parchment paper or Silpat silicone mats.
In a bowl, combine flour with baking soda and salt and set aside.
In a mixing bowl, with a hand mixer cream butter with the sugars until smooth and creamy.
Add an egg, and vanilla extract and beat for 1 minute.
Add in the dry ingredients, and on low-speed mix until just combined. Do not overmix the cookie dough.
With your hands, crush the popcorn so it’s the size of a pea, leaving a few larger pieces. Make sure that there are no unpopped kernels in the popcorn.
With a silicone spatula, fold in the crushed popcorn, and chocolate chips.
Scoop out cookie dough using a small cookie scoop and place on the prepared baking sheets, leaving 2 inches between them.
Bake for 10-11 minutes, allow to cool on cookie sheets for 10 minutes then transfer to a wire rack to cool completely.
Notes
Let these cookies cool on the baking sheets. If you try to remove them too soon they may break.
Don't over-mix the dough. Once you add the dry ingredients to the wet ingredients, mix only until the flour is incorporated.
If you decide to use microwave popcorn, look for a brand that is mostly natural. Movie theatre style or extra butter flavors won't be quite right in this recipe.
Use any kind of baking chips! You need 1 cup of chips in total, so feel free to mix and match. Butterscotch chips, peanut butter chips, or dark chocolate chips will all be tasty in popcorn cookies. Toffee bits would also be amazing!
Fold in the popcorn gently so that you don't break it up even more. My Kitchenaid hand mixer has a very low speed setting that works great for this. If yours doesn't, be sure to mix in the chocolate chips and popcorn by hand with a silicone spatula or wooden spoon.
To Store: Keep these cookies in an airtight container at room temperature for up to 5 days, or in the freezer for up to 1 month.