Double Chocolate Cupcakes

Name: Double Chocolate Cupcakes
Prep time: 40 min
Cook time: 20 min
Total time: 1 h
Cuisine: American
Ingredients: 2 cups all-purpose flour; 3/4 cup unsweetened cocoa powder; 2 cups granulated sugar; 2 teaspoons baking soda; 1 1/2 teaspoons baking powder; 1 teaspoon salt; 1 cup hot milk; 3 large eggs (at room temperature); 1 cup hot coffee; 2 teaspoons vanilla extract; 1/2 cup vegetable oil; 1/2 cup unsalted butter; 1 cup unsweetened cocoa powder; 4 cups powdered sugar; 2/3 cup heavy whipping cream; 4 ounces dark chocolate bar (shaved, optional as garnish)