Preheat the oven to 350 F. Line a 12-cup muffin pan with paper liners. In a medium bowl, whisk together flour, salt, and baking soda.
In a large bowl, combine butter, peanut butter, granulated sugar, and brown sugar until fluffy. Add in the egg and vanilla extract, and mix until smooth.
Add in the flour mixture, mix until it is fully combined. Evenly divide the cookie dough between the prepared liners. Bake for 15-20 minutes. Remove from the oven, and top each cookie cup with one Rolo.