Using a hand mixer, beat the softened butter and sugar together in a medium sized mixing bowl until fluffy.
5 T unsalted butter, 1/4 cup granulated sugar
Add the egg yolk and vanilla, and mix well.
1 egg yolk, 1/4 t vanilla extract
In a separate bowl, or on a sheet of paper, sift the flour, cocoa powder, and baking powder.
2 T dutch cocoa powder, 1/2 cup all purpose flour, 1/4 t baking powder
Add the powder to the butter mixture and use a wooden spoon or a silicone spatula to combine.
Once the dough has come together, place in a gallon size zip bag, and roll out to about 3-5 mm thickness (based on preference, if you want crunchier or softer cookies).
Chill in the refrigerator for one hour.
After chilling, preheat the oven to 350 degrees F, and remove the dough from the bag.
Use small cookie cutters to cut shapes out of the dough.
Place on a cookie sheet with parchment paper. This is a small batch recipe, so using smaller cookie cutters will result in more sandwich cookies.
Bake for 10 minutes. Allow to cool, and move to a wire rack.
Note: roll out the remaining dough, rechill, cut, and bake.
In a small mixing bowl, cream the butter until it is light and fluffy.
3 T unsalted butter
Add a half cup of powdered sugar, along with the orange zest and vanilla, and beat until combined.
1.5 cups powdered sugar, 1 t orange zest, 1/2 t vanilla extract
Add another half cup, mix, and add the remainder and beat until combined.
1.5 cups powdered sugar
Finally, add the orange juice and beat to combine.
4 t fresh squeezed orange juice
Put the buttercream into a small zip bag and cut a small tip off the bottom corner of the bag. Have the cookies prepared, by flipping them over and matching them up.
Pipe the buttercream onto one cookie, and sandwich it with the other cookie.
Place in the refrigerator to chill and harden. Some people say you should never serve buttercream refrigerated, but I think it works great in this recipe, and it keeps it from gushing out the sides. If chilled buttercream isn't your thing, keep it room temperature.
Make sure your cocoa is dutch cocoa, as natural cocoa (such as Hershey's brand) will not work as well.