Prepare the Cookie Dough:

1. Preheat oven to 400°F (200°C). Line two baking sheets with parchment paper.
2. In a medium bowl, sift together flour, cocoa powder, baking soda, and salt.
3. In a large bowl, use an electric mixer to cream together the vegetable shortening, granulated sugar, dark-brown sugar, and butter until light and fluffy.
4. Add the egg, milk, and vanilla extract, mixing until fully combined.
5. Gradually add the dry ingredients to the wet mixture, mixing until just combined.

Bake the Cookies:

6. Using a 1-ounce ice cream scoop or tablespoon, drop small mounds of dough onto the prepared baking sheets, spacing them 1 inch apart.
7. Bake for 10 to 12 minutes, until cookies begin to crack on top and a toothpick inserted in the center comes out clean.
8. Allow cookies to cool completely on a wire rack.

Prepare the Whipped Ganache:

9. Place chopped chocolate in a heatproof bowl.
10. In a saucepan, bring heavy cream to a gentle boil. Pour over the chocolate and let sit for 10 minutes without stirring.
11. Add a pinch of salt, then whisk the ganache until smooth. Let it cool for 45 minutes to 1 hour, stirring occasionally.
12. Using an electric mixer, beat the ganache on medium-high speed until pale and fluffy (about 2 to 4 minutes).

Assemble the Whoopie Pies:

13. Transfer whipped ganache to a piping bag fitted with a ½-inch round tip.
14. Pipe 2 to 2½ teaspoons of ganache onto the flat side of half the cookies.
15. Sandwich with the remaining cookies, pressing gently to spread the filling evenly.