Ingredients:

For the 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