⅓cup(28g)unsweetened or Dutch-process cocoa powder
¼cupheavy cream
Instructions
Preheat the oven to 350 degrees F (or 325 degrees F for convection bake) and line several half sheet pans with parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment (or in a bowl using a handheld electric mixer), add the butter, peanut butter, oil, granulated sugar and powdered sugar. Sprinkle the baking soda, cream of tartar, and salt across the top of the sugars. Mix until well-combined and super creamy, 1-2 minutes, scraping down the sides of the bowl as needed.
Add the sour cream, eggs and vanilla and mix until well-combined, 1-2 minutes, again scraping down the sides of the bowl as needed.
Add the flour (see note below) and mix until no dry streaks remain and the mixture is evenly combined; don't overmix.
Scoop the dough into 2-tablespoon size balls (I use a #40 cookie scoop; you can make them smaller or larger) and roll into balls.
Place the cookies several inches apart on the prepared baking sheets. Lightly spray the bottom of a flat-bottomed glass with cooking spray and dip into granulated sugar. Press each cookie to about 1/4-inch thick. (Repeat dipping the bottom of the glass into sugar as needed.)
Bake the cookies for 7-8 minutes until just set. DO NOT OVER BAKE. In fact, under baking these cookie by just a bit is key.
Let the cookies cool for a few minutes on the baking sheets before removing to a cooling rack to cool completely.
For the frosting, in a medium bowl (can use a handheld or stand mixer) combine the butter, sour cream and vanilla. Mix until thick and smooth and creamy, 1-2 minutes. Add the powdered sugar, cocoa powder, and cream, and mix until well-combined and fluffy, 1-2 minutes. Scrape down the sides of the bowl as needed. Add additional cream, if needed, to adjust the consistency of the frosting so it is thick but still soft and spreadable.
Frost the cooled cookies and decorate with chocolate sprinkles, if desired.
Notes
Peanut Butter: I haven't tried these cookies with natural peanut butter (I've only ever used Skippy or Jif).Cocoa Powder + Powdered Sugar: I like to measure and then sift the powdered sugar and cocoa powder through a mesh strainer into the frosting to prevent lumps.Flour: adding peanut butter to cookie dough has a tendency to dry out the texture of the dough. This cookie dough may seem a little dry after mixing but it should press together in a ball just fine (and bakes up great). However, the amount of flour is also really important. If you live at high elevation, are in a super dry climate, or tend to pack more flour into a measuring cup, you might consider dropping the flour down to 5 cups (if you aren't weighing the ingredients using a kitchen scale, measure with a light hand).