⅓cup(43g)Dutch-process or unsweetened natural cocoa powder
¼ to ⅓cupheavy cream
¼teaspoonvanilla extract
Instructions
Preheat the oven to 350 degrees F. Line several large, rimmed baking sheets with parchment paper.
For the cookies, in a large bowl with a handheld electric mixer or in the bowl of a stand mixer fitted with the paddle attachment, cream together the butter, granulated sugar and powdered sugar until light and creamy, 2-3 minutes. Add the oil, eggs and sour cream and mix until well-combined.
Add the flour, baking soda, baking powder, cream of tartar, and salt. Sift the cocoa powder over the top. Mix until the dough comes together and no dry streaks remain.
Form the dough into balls about 2- to 3- tablespoons each (I use a #20 cookie scoop).
Place the cookies several inches apart on the prepared baking sheet(s).
Place 1/4 cup granulated sugar in a shallow dish. Dip a flat-bottomed glass into the sugar (it helps to rub the bottom of the glass lightly with butter or oil before the first dip so the sugar adheres). Press the glass onto each cookie dough ball, flattening to about 1/4-inch or slightly thicker. Don't press too thin.
Bake for 8-9 minutes until the cookies are set around the edges but still soft in the center. Don't over bake! They should look slightly underdone in the middle. Let them cool for a few minutes on the pan before transferring to a cooling rack to cool completely.
For the frosting, with an electric mixer, cream together the butter and 1 cup of the powdered sugar until very light and fluffy, 1-2 minutes. Add the remaining powered sugar, heavy cream, and vanilla. Sift the cocoa powder over the top (to avoid tiny lumps in the frosting). Mix for 2-3 minutes until very thick and creamy.
Spread the frosting evenly on the cookies. Decorate with sprinkles, if desired. The cookies are delicious cold or at cool room temperature. They can be made several days in advance and kept (frosted and covered) in the refrigerator.
Notes
Update: I've made a few small changes to this recipe to combat the crumbly texture that some have reported. The good news is that the small changes make these cookies better than ever. If you want to know the changes so you can continue to make them the old way here they are: 2016 version: 2/3 cup oil 2023 update: 3/4 cup oil2016 version: 1 1/4 cups sugar 2023 update: 1 1/2 cups sugar2016 version: no sour cream 2023 update: 2 tablespoons sour cream (justification behind this is the crazy popularity of this best-ever Swig cookie recipe)2016 version: 1/2 cup cocoa powder (frosting) 2023 version: 1/3 cup cocoa powder (frosting) *also edited the method a bit to help the mixing come together better.