Chocolate Lover's Chocolate Cake - Once Upon a Chef

Ingredients

• 2 cups all-purpose flour, spooned into measuring cup and leveled off with knife
• 2 cups granulated sugar
• 1 cup unsweetened natural cocoa powder, such as Hershey’s
• 1 teaspoon salt
• 2 teaspoons baking powder
• 1 teaspoon baking soda
• 2 large eggs, lightly beaten
• ½ cup vegetable oil
• 1 cup sour cream
• 1½ teaspoons vanilla extract
• 1 cup boiling water
• 8 ounces semi-sweet or milk chocolate, broken into small pieces (see note)
• 2½ sticks (20 tablespoons) unsalted butter, softened but still cool
• 1¼ cups confectioners' sugar
• ½ cup unsweetened natural cocoa powder, such as Hershey’s
• ⅛ teaspoon salt
• ¾ cup light corn syrup
• 1 teaspoon vanilla extract