Cream-Filled Chocolate Sandwiches

I've been eying this recipe for a while so I decided to give it a try this afternoon. They turned out pretty well, although I would prefer if the chocolate in the cookies shined through more.
The dough is scooped onto cookie sheets and flattened with a sugar-dipped glass.
The baked cookies are set aside to cool.
The filing is whipped until fluffy.
Filling is spread on the bottoms of half of the cookies.
The remaining cookies are placed on top to complete the sandwich.

CREAM-FILLED CHOCOLATE SANDWICHES
From Martha Stewart's Cookies

INGREDIENTS - COOKIES
1 1/4 cups all-purpose flour
3/4 cup unsweetened Dutch-process cocoa powder
1 teaspoon baking soda
1/4 teaspoon baking powder
1/4 teaspoon salt
1 1/2 cups sugar, plus more for flattening cookies
10 tablespoons unsalted butter
1 large egg, room temperature

INGREDIENTS - FILLING
1/2 cup unsalted butter, room temperature
1/2 cup shortening
3 1/2 cups confectioners' sugar
1 tablespoon pure vanilla extract

DIRECTIONS
1. Preheat oven to 375 degrees F. Into a bowl, sift together flour, cocoa powder, baking soda, baking powder, and salt.

2. In the bowl of an electric mixer fitted with the paddle attachment, cream sugar and butter until light and fluffy, about 2 minutes. Add egg; beat to combine. With mixer on low speed, gradually add flour mixture; continue beating until dough is well combined.

3. Using a 1 1/4-inch ice cream scoop, drop dough onto parchment-lined baking sheets about 2 inches apart. Dip bottom of a glass in sugar; press to flatten cookies to about 1/8 inch thick.

4. Transfer to oven and bake until cookies are firm, 8-10 minutes. Remove cookies to wire racks to cool completely.

5. To make filling, combine butter and shortening with an electric mixer. On low speed, gradually add confectioners' sugar and continue beating until light and fluffy, about 2 minutes. Add vanilla and beat to combine.

6. To assemble, place cream filing in a pastry bag and pipe about 1 tablespoon filling onto the flat side of half the cookies. Place remaining cookies on top, and gently press on each to squeeze filling to edges. Filled cookies can be stored in airtight containers at room temperature up to 2 days.