Preheat oven to 350 degrees. Line a large baking sheet with parchment paper or a silicone baking mat.

Use electric mixer to beat brown sugar, sugar, and butter until lightened and fluffy, about 3 minutes.

Mix in eggs, one at a time, scraping down sides as needed. Then, mix in vegetable oil and vanilla extract.

In a small bowl, whisk together flour, cocoa powder, baking soda and salt.

Alternate mixing in flour mixture and buttermilk in 3-4 additions each, beginning and ending with flour mixture.

On prepared baking sheet, drop about 3 tablespoons of batter in a circle shape. Make sure that edges of circles are at least 2 inches apart.

Bake for 10-12 minutes, or until tops of cakes have a cracked appearance and a toothpick inserted into the center one of the center cakes comes out with just a few crumbs.

Let cook on pan for 2-3 minutes before transferring to a cooling rack. Let cool completely before filling.

Heat milk in a saucepan over medium-low heat. Whisk in flour. Whisk continuously until the mixture turns in a thick paste that resembles glue.

Remove from heat and let cool completely.

Once mixture has cooled, use electric mix to mix in butter, peanut butter, salt and vanilla until smooth and creamy.

Mix in powdered sugar. Continue mixing until frosting is smooth and creamy, about 1-2 minutes.

Spread mixture evenly over one side of a cookie. Place a second cook on top of mixture.