Peanut-Butter Sandwich Cookies

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.)