Preheat oven to 350 degrees F. Line a two baking sheets with parchment paper or silicone baking mats. Set aside.
In a medium bowl, whisk together the flour, baking soda, baking powder, and salt. Set aside.
In the bowl of a stand mixer, beat the butter and the peanut butter together until fluffy. Add the sugars and beat until smooth. Add the egg and mix until combined. Add the milk and the vanilla extract and mix again.
Add the flour mixture and beat until flour disappears. Stir in the chopped Snickers and chocolate chips.
Drop by rounded tablespoons onto the prepared baking sheets. Gently flatten each cookie ball with the palm of your hand. Bake for 10-11 minutes, or until cookies are slightly brown on the edges.
Cool the cookies on the baking sheets for about 5 minutes, then remove to a rack to cool completely.