Texas Sheet Cake from Cook's Illustrated

Cake:
2C all purpose flour
2 C sugar
1/2 tsp. baking soda
1/2 tsp. salt
2 large eggs plus 2 yolks
2 tsp. vanilla extract
1/4 C sour cream
8 oz. semisweet chocolate, chopped
4 T butter
3/4 C vegetable oil
3/4 C water
1/2 C cocoa powder
For Icing:
8T butter
1/2 C heavy cream
1/2 C cocoa powder
1T corn syrup
3 c confectioner's sugar
1 C toasted pecans, chopped
For the cake: position oven rack to the middle position and heat oven to 350 degrees F. Grease a 18"X 13" rimmed baking sheet. combine flour, sugar, baking soda, and salt in a large bowl. Whisk eggs and yolks, vanilla, and sour cream in another bowl until smooth. Heat chocolate, butter, oil, water, and cocoa in a large saucepan over medium heat, stirring occasionally, until smooth(3-5 minutes). Whisk chocolate mixture into flour mixture until incorporated. Whisk egg mixture into batter and then pour into prepared baking pan. Bake until toothpick inserted in the center comes clean(18-20 minutes). transfer to a wire rack. For the icing: About 5 minutes before the cake is done, heat butter, cream, cocoa and corn syrup in a 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 pecans. Let cake cool to room temp. on a wire rack, about 1 hour, then refrigerate until icing is set. cake be wrapped and refrigerated for up to 2 days. Bring to room temp. before serving. cut into 3" squares.