For the cookies:
1 3/4 cups all-purpose flour
3/4 cup unsweetened cocoa powder (not Dutch-process)
1 1/2 tsp baking soda
1/2 tsp coarse salt
1 T unsalted butter, softened
1/3 c. vegetable shortening
1/2 cup granulated sugar
1 large egg
1 cup whole milk
1 tsp pure vanilla extract
For the filling:
4 oz cream cheese at room temperature
1/2 cup (1 stick) unsalted butter at room temperature
1/2 cup confectioners' sugar
1/4 cup canned solid pack pumpkin
pinch of cinnamon
pinch of nutmeg
1. Prepare cookies. Preheat oven to 375 degrees. Sift together flour, cocoa, baking soda and salt into a medium bowl; set aside.
2. Place butter, shortening, and sugars into bowl. Mix on high speed until smooth, about 3 minutes. Add egg; mix until pale and fluffy, about 2 minutes. Mix in half the flour mixture, then the milk and vanilla. Mix in remaining flour mixture.
3. Drop about 2 tsp dough onto baking sheets lined with parchment paper, spacing 2 inches apart. Bake until cookies spring back when lightly touched, 12-14 minutes. Transfer baking sheets to wire racks and let cool 10 minutes. Remove cookies from baking sheets and tranfer to wire racks using a spatula. Let cool completely.
4. Prepare filling. In bowl, whip together cream cheese, butter and confectioners' sugar on medium speed until smooth, about 3 minutes. Add pumpkin, butter and nutmeg; whip until smooth, scraping down the bowl as necessary.
5. Pipe or spoon about 2 tsp filling on the flat side of half the cookies. Sandwich with remaining cookies, keeping the flat sides down.