1cupplus 2 Tablespoons (270 mL) whole milk, , room temperature
1teaspoonpure vanilla extract
12Tablespoons(170 g) unsalted butter,, room temperature
1 ¼cups(250 g) granulated sugar
2large eggs,, room temperature
Chocolate Buttercream Frosting
1cup(226 g) unsalted butter,, room temperature
2cups(240 g) confectioners' sugar
½cup(48 g) unsweetened cocoa powder
1teaspoonpure vanilla extract
2-3Tablespoonsmilk
Instructions
Chocolate Sheet Cake
Preheat oven to 350° F. Grease and flour a 9x13 cake pan.
In a medium bowl, whisk together flour, cocoa powder, espresso, baking soda and salt. Set aside.
In a measuring cup, stir together milk and vanilla. Set aside.
In the bowl of a stand mixer or using a hand mixer, beat butter on high speed until light in color, about 1 minute. Add sugar and mix on high until fluffy, about 2 to 3 minutes. Add eggs one at a time mixing well after each addition.
Alternate adding flour mixture and milk to the batter. Add one third of the flour mixture, followed by half of the milk mixture. Repeat and end with remaining flour mixture. Mix just until combined and scrape down the sides and bottom of the bowl as necessary.
Transfer batter to prepare pan and evenly spread it to the corners of the pan. Bake for 22 to 26 minutes or until a toothpick inserted in the center comes out with little to no crumbs. Let cake cool completely before frosting.
Chocolate Buttercream Frosting
Using an electric mixer, beat butter until light and fluffy, about 2 minutes. Place confectioners' sugar and cocoa in a mesh strainer or sifter and sift over the butter. Beat until combined. Add vanilla and 2 Tablespoons milk. Mix until smooth. Add more milk if you'd like a thinner consistency.
Transfer frosting to the cooled cake. Use an offset spatula to spread the frosting over the cake. Cut and serve.
Notes
Store chocolate sheet cake covered at room temperature for 2 days or in the refrigerator for 5 days.Freeze chocolate sheet cake (unfrosted) in a layer of plastic wrap, then aluminum foil. Store on a flat surface in the freezer for up to 1 month. Defrost in the refrigerator before bringing to room temperature and frosting.High altitude adjustments: Decrease sugar by 1/4 cup. Replace espresso powder with 1 Tablespoon espresso or strongly brewed coffee. Increase oven temperature to 360 F. Decrease baking time to 20 to 24 minutes.