Preheat the oven to 350ºF.
Line a baking sheet with parchment paper and set aside.
In a large bow, cream together the melted butter and sugar.
Add in the egg, peanut butter, and vanilla extract, stirring until well combined.
Slowly mix in the baking soda and flour, stirring until well combined.
Using a cookie scoop, place dough onto the baking sheet (or about 1.5 tablespoons worth).
Push down gently on each cookie with a glass or the palm of your hand to flatten it.
Using a fork, press down gently on the cookies to create a criss-cross effect.
Bake cookies for 9-12 minutes.
Let cool 5-10 minutes before transferring to a wire rack to continue cooling.
