Ingredients
1 1/2 sticks unsalted butter, room temperature
1 cup old-fashioned rolled oats
1 cup plus 2 tablespoons unbleached all-purpose flour
1 teaspoon baking soda
1 teaspoon kosher salt
1/2 cup packed dark-brown sugar
1/3 cup granulated sugar
1/2 cup smooth peanut butter
Turbinado sugar, for sprinkling
4 tablespoons unsalted butter, room temperature
3/4 cup smooth peanut butter
1/4 cup confectioners’ sugar, sifted
1/2 teaspoon kosher salt
Preparation
Cookies: In a saucepan over medium heat, melt 1/2 stick butter. Add oats and cook, stirring, until toasted, 5 to 10 minutes. Spread mixture onto a parchment-lined baking sheet; let cool completely.
In a bowl, whisk together flour, baking soda, and salt. Beat remaining 1 stick butter with granulated and brown sugars on medium-high speed until pale and fluffy, about 3 minutes. Add peanut butter; beat until well combined.
Gradually add oat mixture and flour mixture; beat on low speed until combined. Roll out dough between 2 sheets of parchment 1/4 inch thick. Slide dough with parchment onto baking sheet and refrigerate until chilled, about 20 minutes.
Preheat oven to 350 degrees. Remove top layer of parchment; cut out cookies using a 2-inch round cookie cutter. Place cookies on parchment-lined baking sheets, spaced about 1 inch apart; sprinkle with turbinado sugar. Bake until golden, about 10 minutes. Let cool completely on sheets.
Filling: In a medium bowl, beat all ingredients on medium speed until smooth. Transfer mixture to a pastry bag fitted with a 1/2-inch round tip (such as Ateco #806).
Pipe filling in a spiral motion on bottom sides of half of cookies. Top with remaining cookies to form sandwiches. (Filled cookies can be stored in an airtight container at room temperature up to 3 days.)
