The cookies on top are made from the same wafer batter as the actual cake and decorated with royal icing.
- 2 1/2 cups all-purpose flour, plus more for parchment
- 3/4 cup unsweetened Dutch-process cocoa powder
- 1/2 teaspoon salt
- 1 teaspoon baking powder
- 1 teaspoon baking soda
- 1 cup (2 sticks) unsalted butter, softened
- 1 1/3 cups packed light-brown sugar
- 2/3 cup granulated sugar
- 2 large eggs
- 2 teaspoons pure vanilla extract
- 3 cups heavy cream
- 1/4 cup confectioners' sugar
- Royal Icing
Sift flour, cocoa, salt, baking powder, and baking soda in a bowl. Mix butter and brown and granulated sugars on medium speed until pale and fluffy. Mix in eggs and vanilla. Reduce speed to low. Add flour mixture; mix until just combined.
Divide dough into quarters; shape into squares. Wrap each in plastic; refrigerate until firm, about 30 minutes. Working with 1 square at a time, roll out dough between pieces of lightly floured parchment to 12-inch square, about 1/8 inch thick. Transfer on parchment to baking sheet; freeze until firm, about 20 minutes.
Preheat oven to 350 degrees. Cut dough into rounds with 2 1/4-inch cutter and into moon and stars with shaped cutters. (You will need 75 rounds for the cake; use remaining dough as desired.) If dough becomes too soft, freeze for a few minutes. Space cookies 1 1/2 inches apart on baking sheets lined with parchment. Freeze until firm, about 15 minutes.
Bake until centers are firm to the touch, 10 to 12 minutes. Transfer to wire racks to cool. Can be stored in airtight containers at room temperature up to 1 week.
Beat cream and confectioners' sugar until soft peaks form.
Lay 15 cookies in an 8-inch circle, overlapping edges slightly to fill the circle. Spread with about 11/4 cups whipped cream. Repeat, making 5 layers. Refrigerate at least 6 hours or up to 1 day.
Tint royal icing as desired. To frost moon and star cookies, pipe icing around edges; pipe zigzags to fill in, and spread with small offset spatula. Let stand until set, 1 to 2 hours. Serve cake, garnished with moon and star cookies.