Cream the butter on medium-high speed for two minutes. Add the sugars and cream for another 3 minutes.
Add the eggs, one at a time, and beat for another minute, scraping the bowl. Add vanilla.
Add the flour, baking soda, baking powder, and salt. Mix on low until the dough just comes together. Add the Snickers and mix just to incorporate.
Chill for one hour, or up to two days.
Preheat oven to 350°. Line two baking sheets with parchment paper. Roll dough into walnut size balls. Place 3 inches apart on baking sheet. Bake for 10 to 12 minutes. You want them to be just set and lightly brown on the edges. Let cool for 2 to 3 minutes, then transfer to a rack to cool.
Let the pans cool completely and bake the remaining cookies. This recipe makes about 3 dozen cookies.