Preheat your oven to 350°F (175°C). Line a cupcake pan with cupcake liners.
In a large mixing bowl, combine the 3 large eggs, 3/4 cup sour cream, 3/4 cup vegetable or canola oil, and 1 tablespoon vanilla extract. Mix until well combined.
Pour in the 1 box of Super Moist Chocolate Fudge Cake Mix and the 1 package of instant chocolate pudding mix. Stir until the dry ingredients are fully incorporated.
Carefully mix in the 1/2 cup of hot water or coffee. This helps to create a smoother batter and enhances the chocolate flavor.
Fold in the 1 cup of mini chocolate chips or chopped chocolate bar.
Spoon the batter into the prepared cupcake liners, filling them about two-thirds full.
Place the cupcake pan in the preheated oven and bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, remove the cupcakes from the oven and let them cool in the pan for about 5 minutes. Then transfer them to a wire rack to cool completely.
In a mixing bowl, beat 20 tablespoons of room temperature unsalted butter until creamy. Gradually add 3 cups of powdered sugar and 3/4 cup of Dutch process cocoa powder. Pour in 3 tablespoons of heavy cream, 1 teaspoon of vanilla extract, and 1/16 teaspoon of salt. Beat until light and fluffy.
Once the cupcakes are completely cool, generously frost each cupcake with the chocolate frosting using a spatula or a piping bag.