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 with peanut butter and sugar until fluffy.
Add in egg and vanilla extract, and mix until smooth. Add in the flour mixture and mix until it is fully combined. Evenly divide the peanut butter cookie dough between the prepared muffin pan.
Bake for 12-15 minutes. Remove from the oven and decorate each cookie cup with pretzels, chocolate chips, and m&ms.
