Preheat the oven to 350 F. In a medium bowl, whisk together flour, salt, and baking soda. In a large bowl, combine butter, peanut butter, and both sugars until fluffy.
Add in the egg and vanilla extract, and mix until smooth. Add in the flour mixture, and mix until it is fully combined. Fold in the snickers bars.
Evenly press the cookie dough into a greased 8-inch square baking dish. Bake for 20-25 minutes.