These peanut butter sandwich cookies with a peanut butter filling are the perfect treat.
Melt 4 tablespoons butter in a medium saucepan over medium heat. Add oats and cook, stirring, until toasted, around 4 minutes. Be careful, as oats begin to toast quickly. Spread oat mixture onto a plate and let cool.
Line 2 baking sheets with parchment paper; set aside.
In a medium bowl, whisk together flour, baking soda, and salt. Set aside. In a separate medium bowl, use an electric mixer to cream together remaining ½ cup butter, granulated and brown sugars. Add peanut butter and mix until well combined.
Add oat mixture and flour mixture; mix until combined. Turn dough out onto a piece of parchment paper. Cover dough with another piece of parchment paper and roll out dough to 1/4 inch thick over the upper parchment paper. Transfer to a refrigerator until chilled, about 20 minutes.
Preheat oven to 350 degrees.
Remove top layer of parchment paper. Cut out cookies using a 2-inch round cookie cutter. Place cookies 1 inch apart on prepared baking sheets; sprinkle with sugar.
Bake until golden, rotating baking sheets at 5-minute mark, halfway through baking, 10 minutes. Let cool completely on baking sheets.
In a medium bowl, mix all ingredients together with an electric mixer on medium speed.
Assemble the sandwich cookies:
When cookies have cooled completely, use a spatula to spread peanut butter filling onto half of the underside of cookies. Top with other half of cookies to make sandwiches.