1-Preheat the oven to 350°F: Preheat the oven to 350°F. Grease a jelly roll pan (12×17) and set aside.
2-In the bowl of a stand mixer,: In the bowl of a stand mixer, beat together the butter and 1 cup of peanut butter until fluffy and well blended. Scrape down the sides of the bowl.
3-Add granulated sugar and brown sugar to: Add granulated sugar and brown sugar to the butter mixture and beat well (1 to 2 minutes).
4-Add in the eggs and vanilla extract: Add in the eggs and vanilla extract and beat on medium-high for another 2 to 3 minutes, scraping down the sides and bottom of the bowl intermittently to ensure even mixing.
5-In a separate bowl, stir together the: In a separate bowl, stir together the salt, baking soda, flour, and oats.
6-Add the flour mixture to the creamed: Add the flour mixture to the creamed ingredients and beat just until combined (do not overmix).
7-Use a spatula or greased hands to: Use a spatula or greased hands to pat the cookie dough into the prepared sheet pan.
8-Bake for 16 minutes, until the center: Bake for 16 minutes, until the center is set and the edges of the cookie are golden brown. Remove from the oven.
9-In a microwave-safe bowl, heat the remaining: In a microwave-safe bowl, heat the remaining 1 cup of peanut butter for 30 seconds to 1 minute until it is mostly melted and easily spreadable. Pour the melted peanut butter over the baked cookies and spread to the edges. Allow the cookies to cool completely. Once room temperature, you can place the pan into the refrigerator to help the peanut butter set again and make it easier to frost.
10-To make the frosting, beat the butter: To make the frosting, beat the butter with an electric mixer.
11-Add the cocoa powder, powdered sugar, vanilla: Add the cocoa powder, powdered sugar, vanilla extract, and a pinch of salt. The mixture will be very dry.
12-Drizzle the heavy cream into the bowl: Drizzle the heavy cream into the bowl with the mixer running and beat until light and fluffy.
13-Spread frosting over the cooled peanut butter: Spread frosting over the cooled peanut butter cookie base.
14-Cut into bars and serve: Cut into bars and serve.