Pre-heat oven to 350° and line two baking sheets with parchment paper.
To a mixing bowl add flour, cocoa powder, baking soda and salt. Mix well and set aside.
To another mixing bowl add melted butter, egg, sugars and vanilla. Beat until combined. Add the dry ingredients to the wet ingredients and mix. Fold in the chopped chocolate.
Cover and chill the dough for 30 minutes. Using a tablespoon drop dough onto prepared baking sheets two inches apart. Bake for 12 minutes. Sprinkle with flaky salt and let cool on baking sheet for five minutes and then transfer to a wire rack to completely cool.
While the cookies are cooling, make the filling. To a large mixing bowl add cream cheese, butter, pumpkin puree, cinnamon and nutmeg. Mix the filling using a hand mixer and slowly add the icing sugar, half cup at a time until everything is incorporated.
Once cookies have cooled and you have the filling ready, make the cookie sandwiches by smearing one to two tablespoons of the filling in between two cookies. Enjoy!