Special equipment: a pastry bag fitted with a round tip
For the Moustache Os: Preheat the oven to 350 degrees F.
Sift together the sugar, flour, cocoa powder, baking soda, baking powder and salt. Pour the sifted mixture into the bowl of an electric stand mixer fitted with the beater attachment.
Slowly beat in the butter and then beat in the egg. Mix the dough until all of the butter is evenly distributed and a ball forms. The dough should appear slightly darker in color.
Portion out the dough into 24 balls (they should be about 48 gram (1.7 ounces) each) using a small ice cream scoop or your hands and place on a greased baking sheet. Bake the cookies until they are crisp on the edges but still slightly chewy in the center, about 8 to 10 minutes. Let cool.
For the filling: Beat the butter in the bowl of the stand mixer fitted with the beater attachment until the color changes from yellow to white, 3 to 5 minutes. Add in the sugar in small amounts.
Slowly incorporate the cream until the frosting sticks to your fingers when you touch it. If the frosting doesn't stick, gradually incorporate another splash of cream.
Add the salt and vanilla bean seeds and beat until fully incorporated and the filling is creamy and light.
To assemble: Pipe the filling onto 12 of the cookies. Top with the remaining 12 cookies.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.