Texas Sheet Cake

Ingredients

• 2 cups all-purpose flour
• 2 cups white sugar
• 1 teaspoon baking soda
• ½ teaspoon salt
• ½ cup sour cream
• 2 eggs
• 1 cup butter
• 1 cup water
• 5 tablespoons unsweetened cocoa powder
• 6 tablespoons milk
• ½ cup butter
• 4 cups confectioners' sugar
• 1 teaspoon vanilla extract
• 1 cup chopped walnuts (Optional)