Step 1

In a small bowl, whisk together the flour, cocoa powder, baking soda, and salt. In the bowl of a stand mixer fitted with the paddle attachment, mix the butter, confectioners' sugar, and vanilla extract. Cream together on medium speed for a minute, then add the flour mixture and mix just until evenly combined.

Step 2

On a sheet of plastic wrap, form the dough into a 1 1/2-inch-thick log. Wrap and refrigerate until firm, at least 1 hour. The cookie dough can be made the day before.

Step 3

Preheat the oven to 350°F and line 3 baking sheets with parchment paper. Using a sharp knife, slice the dough log into thin rounds, about 1/8-inch-thick. Arrange on the baking sheets and bake for about 8 minutes or until set (they will no longer be shiny). If baking more than one sheet at a time, you may want to rotate the trays back to front and switch from top to bottom racks midway through baking. Let the cookies cool completely. Makes about 75 cookies.

Step 4

In a medium saucepan, put the sugar in a mound in the center of the pan, being sure it doesn’t hit the sides. Gently add the corn syrup and 1/4 cup water, making sure the sugar doesn’t splash up on the sides of the pan. Cook over high heat, without stirring.

Step 5

When the sugar starts to color on the edges, gently stir the sugar until it is quite dark and smokes a bit. Once the caramel is dark, reduce the heat and slowly add half the cream. The caramel will sputter and seize up, which is normal. Gently whisk the caramel until the caramelized sugar dissolves. Add the remaining cream and stir.

Step 6

Pour the caramel cream into a bowl. Cover and refrigerate until well chilled, at least 2 hours. This can be made a day ahead.

Step 7

To assemble, line an 8 x 4-inch loaf pan with plastic wrap. Set aside.

Step 8

In the bowl of a stand mixer fitted with the whisk attachment, whip the chilled caramel cream until very soft, slouchy peaks form.

Step 9

Coat the bottom of the prepared pan with about a 1/4-inch-thick layer of the cream. Line the outside of the pan with some of the cookies. Spread a layer of the cream on each cookie and layer them together in the pan vertically. You should end up with about 3 rows of cookies and cream. This may vary slightly depending on how large your cookies are. Cover the top with more cream, so the cookies are completely covered. Next add a layer of cookies, this time laying them over the cream horizontally. Add two more layers of cream and cookies, ending with a layer of cream. Cover with plastic wrap and refrigerate the cake for at least 6 hours, but ideally overnight.

Step 10

To make the topping: After the cake has chilled, in a stand mixer fitted with the whisk attachment, whip the heavy cream, confectioners’ sugar, and vanilla on medium speed until just stiff (do not over beat). Taste and adjust the sweetness to your liking by beating in more sugar.

Step 11

Invert the icebox cake onto a serving platter. Frost the top and sides of the cake with the whipped cream. If desired, pipe a design on the top of the cake using a pastry bag fitted with a rose tip or other piping tip. Top with chocolate shavings. Serve immediately or refrigerate until ready to serve.