Homemade Oreo Cookies

Preheat oven to 350 ℉.
Sift together the flour, cocoa powder, baking soda, and salt. Place in the bowl of a food processor.
Add the chilled and cubed butter and the white and brown sugars to the food processor and pulse until it resembles coarse meal. Add the egg and continue to pulse until a dough forms.
Roll the dough between two pieces of parchment paper or on a lightly floured surface until 1/4 inch thick and cut out cookies with a 2-inch scalloped edged round cookie cutter, or any of your favorite cutters.
Bake for 12-15 minutes. Cookies will be soft at first, but harden as they cool.
In the bowl of a standing mixer or with an electric mixer, cream together the shortening and butter, then gradually add the powdered sugar until the filling is soft and fluffy.
Spread 1 teaspoon of filling onto half of the cookies and sandwich together with the remaining cookies.