Preheat oven to 325 degrees and line two baking sheets with parchment paper.
Microwave a bag of popcorn or pop it yourself, salt and butter it. Set aside.
In a large bowl or stand mixer beat butter and sugars for about 2 minutes until fluffy.
Add the vanilla, salt, baking soda, 1 whole egg and only the yolk from second egg. Discard the egg white or use for something else. Mix for another 1-2 minutes until combined.
Slowly add in your flour into the bowl and mix for another 1-2 minutes.
With a spatula stir in M & M's and fold in popcorn.
Scoop cookie dough into mounds on cookie sheet about 2 tablespoons each and 9 cookies per sheet. Bake cookies until golden brown, about 14 minutes. Transfer to a cooling rack and let cool.