Preheat oven to 350 degrees. Line two baking sheets with parchment paper, set aside. In a stand mixer with the paddle attachment cream butter and both sugars until light and fluffy, about 3 minutes.
Add in peanut butter and mix for 1-2 minutes. Add in egg and vanilla. Mix until combined.
Add in flour, salt and baking soda and mix just until combined. Make sure not to overmix.
Fold in the 3/4 cup of Reese's and mix to combine.
Portion into heaping tablespoon cookies and place on the prepared baking sheet.Bake cookies for 8-10 minutes or until lightly golden brown and firm on the edges. Remove from the oven and allow the cookies to cool on the baking sheet for 5 minutes before transferring to a cooling rack to cool completely. Place remaining 1/4 cup of reese's on top of the warm cookies.