Homemade Oreos®

I absolutely love Oreos, they're a bit time consuming, but very worth it. Enjoy!

Ingredients:
Cookies 
1¼ cups  flour
½ cup cocoa
1 tsp baking soda
¼ tsp baking powder
¼ tsp salt
1¼ cups sugar
½ cup plus 2 tbs unsalted butter
1 egg
Filling
¼ cup unsalted butter¼ cup shortening
2 cups powdered sugar
2 tsp vanilla

Directions: 
Heat oven to 375˚F. In a food processor, thoroughly mix the flour, cocoa, baking soda and powder, salt, and sugar. While pulsing add the butter, and then the egg. Continue processing until dough comes together. Take rounded teaspoons of the dough, and roll them into round balls, then place them about 2 inches apart on a parchment-lined baking sheet. Slightly press down the rounds into disks. Then refrigerate the sheet for 10 minutes. Once the dough is chilled, bake the sheets for 6-8 minutes, just until the tops are cracking. Let the cookies cool on a wire rack. 
Prepare filling, place butter and shortening in a mixing bowl, and at low speed, gradually beat in the sugar and vanilla. Turn the mixer on high and beat for 2 to 3 minutes until filling is light and fluffy. 
Put filling in a pastry bag and pipe a thin layer on half of the cookies and place another cookie on top to form the sandwich.