Cream the butter, sugar, and cocoa powder together in a large mixing bowl until well blended. Add the cornstarch and flour and mix the dough together until thoroughly combined. Cover tightly and refrigerate for at least 2 hours, or longer if desired.
Preheat oven to 350°F.
Form small heaps with the dough on a parchment lined baking sheet. I used a 1" scoop. Bake for about 13 minutes. Cool slightly on the pan, and then on a rack. Be careful, these cookies are delicate.
Mix the soft butter with the cocoa powder and sugar, then add the rest of the ingredients and mix well, until smooth and creamy. Top each cooled cookie with a generous blob of frosting, and dust with powdered sugar.
Nutritional information is provided as a courtesy and is an estimate only. This information comes from online calculators. Although The View from Great Island attempts to provide accurate nutritional information, these figures are only estimates.
Did You Make This?We love seeing what you've made! Tag us on social media at @theviewfromgreatisland for a chance to be featured.