Preheat the oven to 350℉.
In a medium bowl, mix together the flour, baking soda and salt.
In a separate bowl, beat together the peanut butter and butter until smooth. Add in the sugar, egg and vanilla until light and fluffy.
Slowly add in the flour mixture and mix until fully combined.
Roll the dough into small balls and place in the cavities of a mini muffin pan.
Make an indent in the center of each dough ball and place an unwrapped peanut butter cup into each.
Bake in the preheated oven for 8-10 minutes.
Remove and let cool on wire racks.