Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper.
Soften the butter in the microwave for about 20 seconds till soft but not melted.
In a bowl, mix together the softened butter, creamy peanut butter, brown sugar, and white sugar until smooth.
Add the egg and vanilla extract, mixing well until evenly blended.
Gradually stir in the unbleached flour, baking powder, and baking soda until a dough forms.
Scoop out about 2 tablespoons of dough for each cookie, shaping them into balls on the baking sheet.
Create a criss-cross pattern on top of each cookie using a fork.
If desired, sprinkle with sea salt.
Bake for 9 minutes, until pale and slightly under-baked. They will continue to cook as they cool.
Let cookies cool on the baking sheet for 15 minutes, then transfer to a cooling rack.