For the cake
6 tablespoons (84 g) unsalted butter, at room temperature
6 tablespoons (72 g) Spectrum nonhydrogenated vegetable shortening, at room temperature
1/4 cup + 2 tablespoons (72 g) granulated sugar
3/4 cup (164 g) packed light brown sugar
1 tablespoon pure vanilla extract
1 egg (50 g, weighed out of shell) + 2 egg yolks (50 g) at room temperature, beaten
1 teaspoon baking soda
1/2 teaspoon kosher salt
1 1/2 cups (10 ounces) semi-sweet chocolate chips
2 cups (280 g) high-quality all-purpose gluten-free flour (I used Better Batter)
1 teaspoon xanthan gum (omit if your blend already contains it)
For the frosting
10 tablespoons (140 g) unsalted butter, at room temperature
1/4 cup (2 fluid ounces) milk, at room temperature
1 tablespoon pure vanilla extract
1/8 teaspoon kosher salt
2 teaspoons meringue powder
4 cups (460 g) confectioners’ sugar
Preheat your oven to 325°F. Line a 12-inch pizza pan with unbleached parchment paper and set it aside.
In a large bowl, place the butter, shortening, granulated sugar, brown sugar, and vanilla, and beat until well-combined with a handheld mixer. Add the beaten egg and yolks, baking soda, and salt, and beat again until well-combined. Add the chocolate chips to the flour blend, toss the chips in the flour to coat them in flour, and then add them both to the bowl. Mix until combined. The dough will be thick but soft.
Scrape the dough out onto the prepared pizza pan, and, with wet hands, press it into a disk. Slide the parchment with the cookie dough on it off of the pizza pan, cover with another piece of unbleached parchment paper, and roll out the dough between the parchment until it is a round about 1/2 inch thick, about 10 inches in diameter. Remove the top sheet of parchment paper and slide the bottom parchment with the cookie dough back onto the pizza pan. There should be a 2 inch wide border all around the perimeter of the cookie dough between the dough and the edge of the pizza pan. The cookie will spread during baking.
Place the pizza pan in the center of the preheated oven and bake, rotating once, for about 20 minutes or until lightly golden brown all over. Allow to cool on the baking sheet until firm, about 5 minutes. Transfer to a wire rack to cool completely.
While the cookie cake is cooling, make the frosting. In the bowl of your stand mixer fitted with the paddle attachment or a large bowl with a handheld mixer, place the butter and mix on medium speed until light and fluffy. Add the milk and vanilla, and turn the speed to mix until very creamy. Add the salt, meringue powder and about 3 1/2 cups of confectioners’ sugar. Mix slowly until the sugar is incorporated, then turn the mixer up to high and beat until it becomes uniformly thick. Add the rest of the confectioners’ sugar if necessary to thicken the frosting.
Once the cookie cake is completely cool, decorate the cookie cake with the frosting. Leave about 2/3 of the frosting white and place it in a piping bag fitted with a large open star tip. Use that frosting to make the stars around the border. Then, mix some blue gel food coloring into the remaining 1/3 frosting and placed it in a piping bag fitted with a small open round tip. Use the blue frosting for writing a message in the center of the cake, and then fill in the rest of the open spaces with more stars using the remaining white frosting. Allow the frosting to set at room temperature until it hardens a bit. Store any leftovers in an airtight container at room temperature.
Originally posted on the blog in 2013. Photos, much of the text, and video all new; recipe largely unchanged (method altered).