Horchata Sheet Cake

 

21/2 C. (312 g) unbleached all-purpose flour

2 1/2 tsp. baking powder

1 tsp. ground cinnamon

1/2 tsp. Diamond Crystal kosher salt or 1/4 tsp. fine sea salt

3/4 C. (12 T./170 g) unsalted butter, at room temperature

1 3/4 C. (350 g) sugar
2 tsp. pure vanilla extract

3 large eggs
1 1/3 C. (305 g) buttermilk

 

6 T. (47 g) unbleached all-purpose flour

1 1/2 C. (300 g) sugar

1/4 tsp. Diamond Crystal kosher salt or 1/8 tsp. fine sea salt

1 1/2 C. (354 g) horchata (from your favorite taquería)

1 1/2 C. (342 g) unsalted butter, at room temperature

1 tsp. vanilla bean paste

1 1/2 tsp. ground cinnamon

 

2/3 C. (157 g) horchata (from your favorite taquería)

 

Make the cake: Preheat the oven to 350°F (180°C). Lightly grease a 9 × 13-inch (23 × 33 cm) cake pan.  In a medium bowl, whisk together the flour, baking powder, cinnamon, and salt and set aside.  In a stand mixer fitted with the paddle, beat the butter with the sugar on medium speed for 2 1/2 minutes, until light and fluffy and paler in color. Add the vanilla and eggs, one at a time, beating well after each addition. Add one-third of the dry ingredients, mix on low to incorporate, then one-third of the buttermilk, followed by another third of the dry mixture, another third of the buttermilk, and then finally the last amount of each. Mix just until combined, then use a silicone spatula to scrape down the sides of the bowl to make sure everything’s mixed in. Scrape the batter into the prepared pan, smooth it out, and bake until the cake is lightly golden brown and a toothpick or skewer inserted into the center of the cake comes out clean, 30 to 35 minutes. Let the cake cool completely in the pan. Make the buttercream: In a small saucepan, combine the flour, sugar, and salt. Whisk in the horchata until everything has been fully incorporated. Set over medium-low heat and bring the mixture to a boil, whisking occasionally to make sure it doesn’t burn. Once it reaches a boil, reduce the heat and continue whisking until the pudding has thickened, about 2 minutes. Use a silicone spatula to transfer the pudding to a plate and immediately press plastic wrap onto the surface to prevent a skin from forming. Let it cool for a few minutes, then refrigerate for about 1 hour or until it has cooled completely.   In a stand mixer fitted with the whisk, beat the butter on medium speed with the vanilla and cinnamon for a minute. With the mixer on low, add the cooled pudding mixture 1 T. at a time until it’s all been added to the bowl, then boost the speed to medium-high and beat until the frosting is light and fluffy, 2 to 3 minutes.   Soak the cake: Use a toothpick to poke small holes on the surface of the cake, then drizzle the horchata over the cake to soak. Spread the frosting evenly over the cake. Return the cake to the refrigerator for 30 to 45 minutes to firm up the frosting. (This makes for a clean cut, and to me, cold buttercream just tastes so much better!)