Whisk together flour, baking soda, and kosher salt.
Mix sugars with peanut butter and unsalted butter until creamy.
Beat in vanilla extract and the egg.
Mix in the chopped fresh rosemary.
Wrap the dough in plastic cling film. Chill at least 2 hours.
Line two baking sheets with parchment paper. Preheat the oven to 350F.
Pour the sugar or rosemary-flavored sugar out onto a flat plate.
Form 1" dough balls, roll in the sugar, and place on a baking sheet. Use a fork to flatten the cookie and create a criss-cross pattern on top.
Bake 8 minutes or until the cookies start to turn light golden brown.
Transfer to a wire rack. Let cool completely.
*To make Rosemary Sugar:
Combine 1/4 cup white granulated sugar with one teaspoon of finely chopped rosemary in a sealed jar for one week. Shake occasionally. The sugar will be scented with the flavor of rosemary.