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1
Preheat the oven to 350F.
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2
To make the cookies, melt 4 tablespoons of the butter in a saucepan over medium heat.
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3
Add the oats and cook, stirring frequently, for 5 to 7 minutes, until toasted.
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4
Pour the toasted oats onto a sheet pan and let cool.
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5
Combine the remaining 1/2 cup butter and the sugars in a stand mixer with the paddle attachment and mix until there are no chunks of butter left.
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6
Add the peanut butter and mix until combined.
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7
On low speed, add the toasted oats, then the flour, baking soda, and salt and blend into a smooth dough.
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8
Chill the dough in the freezer for 5 minutes.
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9
Transfer the dough to a large surface covered with a layer of parchment paper.
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10
Top with another layer of parchment and gently roll the dough into a 1/4-inch-thick sheet.
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11
To prevent the cookies from sticking as you cut them, carefully remove the top layer of parchment and sprinkle some flour over the sheet of dough.
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12
Replace the parchment, flip the dough, and release the parchment on the other side.
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13
Cut the dough into 2 1/2-inch round cookies and space about 1/2 inch apart on an ungreased cookie sheet.
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14
Gather any leftover scraps of dough and roll and cut as described above.
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15
Repeat until you have no dough left.
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16
Bake the cookies for about 20 minutes, turning the pan 90 degrees halfway through baking, until golden in color.
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17
Transfer the cookies to a cooling rack.
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18
Let cool completely before filling.
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19
To make the filling, combine the butter, salt, sugar, and peanut butter in the bowl of a stand mixer with the paddle attachment.
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20
Mix on medium speed until the filling is smooth.
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21
Place half of the cookies with the top side (the most attractive) down.
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22
Using a piping bag or a spoon, evenly distribute the filling among those cookies, and close into sandwiches with the remaining cookies.
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23
Gently press down.
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24
Serve immediately or store the cookies in a cool place.
