Chocolate Sheet Cake with Milk Chocolate Frosting

Ingredients

• 1 ½ cups sugar
• 1 ¼ cups flour
• ½ teaspoon baking soda
• ½ teaspoon salt
• 1 cup milk
• 8 ounces bittersweet chocolate, chopped fine
• ¾ cup Dutch-processed cocoa powder
• 2/3 cup vegetable oil
• 4 large eggs
• 1 teaspoon vanilla extract
• 1 pound milk chocolate, chopped
• 2/3 cup heavy cream
• 16 tablespoons unsalted butter, cut into 16 pieces and softened

Directions

1. Heat oven to 325 degrees. Lightly spray a 13 by 9 inch baking pan with vegetable oil spray. Whisk sugar, flour, baking soda, and salt together and set aside.
2. Combine milk, chocolate and cocoa in a large saucepan. Place saucepan over low heat and cook, whisking frequently, until chocolate is melted and mixture is smooth (may do this in the microwave carefully). Remove from heat and let cool slightly.
3. Whisk oil, eggs, and vanilla into the chocolate mixture (mixture may initially look curdled) until smooth and homogenous. Add sugar mixture and whisk until combined, making sure to scrape the corners of the saucepan.
4. Transfer batter to prepared pan. Bake until firm in the center when lightly pressed and a toothpick inserted in the center comes out with a few crumbs attached, 30-35 minutes. Let cake cool completely in pan on a wire rack before frosting, 1-2 hours.
5. For the frosting: combine chocolate and cream in a large heatproof bowl over a saucepan filled with 1 inch of barely simmering water, making sure the water does not touch the bottom of the bowl. Whisk mixture occasionally until chocolate is uniformly smooth and glossy, 10-15 minutes.
6. Remove bowl from saucepan. Add butter, whisking once or twice to break up the pieces. Let mixture stand for 5 minutes to finish melting the butter, then whisk until completely smooth. Refrigerate frosting without stirring until cooled and thickened, 30 minutes to 1 hour. Once cooled, whisk frosting until smooth.
7. Spread frosting evenly over the top of the cake. Cut cake into squares and serve out of the pan.