Preheat the oven to 350 degrees.
Line two baking sheets with parchment paper.
In a medium mixing bowl, mix together the butter and peanut butter until smooth.
Add the sugar and brown sugar and mix until well incorporated.
Add the egg and vanilla and mix until smooth.
In a separate bowl, whisk together the flour, salt, and baking soda.
Add the dry ingredients to the wet mixture and mix JUST UNTIL ALL THE FLOUR IS INCORPORATED.
Using a large cookie scoop, place dough balls on the prepared baking sheet spaced 2-3 inches apart. Or, if using your hands, shape the dough into walnut-sized balls and place them two inches apart on the cookie sheet.
Bake large cookies for 12-13 minutes or walnut sized for 10-12 minutes. They're done when the edges look set, but not brown. The color of the cookie should be uniform all the way around.
Let the cookies cool at least 15 minutes before removing them from the baking sheet.
Enjoy!