Cook's Country Texas Sheet Cake

Cake

2 cups all-purpose flour

2 cups sugar

1/2 teaspoon baking soda

1/2 teaspoon salt

2 large eggs plus 2 yolks

2 teaspoons vanilla extract

1/4 cup sour cream

8 ounces semisweet chocolate, chopped

4 tablespoons unsalted butter

3/4 cup vegetable oil

3/4 cup water

1/2 cup Dutch-processed cocoa powder

Chocolate icing

8 tablespoons unsalted butter

1/2 cup heavy cream

1/2 cup Dutch-processed cocoa powder

1 tablespoon light corn syrup

3 cups confectioners' sugar

1 tablespoon vanilla extract

1 cup toasted pecans, chopped

Preheat oven to 350ºF. Grease an 18x13-inch rimmed baking sheet. Set aside.

Combine flour, sugar, baking soda, and salt in a large owl. In another bowl, whisk eggs, yolks, vanilla, and sour cream until smooth.

Heat chocolate, butter, oil, water, and cocoa powder in medium saucepan over medium heat, stirring occasionally, until smooth, 3 to 5 minutes. Whisk the chocolate mixture into the flour mixture until incorporated. Whisk egg mixture into the batter, then pour into prepared baking pan. Bake until toothpick inserted into center comes out clean, 18 to 20 minutes. Set on wire rack.

About 5 minutes before cake is done, heat butter, cream, cocoa, and corn syrup in large saucepan over medium heat, stirring occasionally, until smooth. Off heat, whisk in confectioners’ sugar and vanilla. Spread warm icing evenly over hot cake and sprinkle with nuts. Let cake cool to room temperature on wire rack, about 1 hour, then refrigerate until icing is set, about 1 hour longer. (Cake can be wrapped in plastic and refrigerated for up to 2 days. Bring to room temperature b