Preheat oven to 375°F and line cookie sheet with parchment paper.
Cream together the butter and sugars in a stand mixer or with a hand held mixer until fluffy. About 2 minutes total. Add the egg and mix in to combine. Add peanut butter and vanilla and mix until smooth and creamy.
In a bowl whisk together the flour, salt and soda and add to wet mixture. Mix this in JUST until combined. It is important to not over mix.
Using a small cookie scoop, scoop dough into balls. This is about 1 ½ inches of dough or one Tablespoon. Roll in sugar and place on prepared cookie sheet. Leaving about 2 inches between scoops.Bake at 375℉ for about 8-9 minutes. They should just be starting to crack and appear done on the sides. It is super important not to over bake!
Immediately press a candy into center of each cookie; cookie will crack around edges. Let cool for 2 minutes then remove from cookie sheet to wire rack. Cool completely.
Notes
Bake just until starting to crack. Baking too long will dry out the cookies.