1. Preheat the oven to 350°F and line a 12-cup muffin pan with cupcake liners.

2. Whisk together the flour, cocoa powder, baking powder, baking soda, and salt in a medium bowl.

3. In a large bowl, whisk the eggs, granulated sugar, and brown sugar until smooth.

4. Add the oil, sour cream, milk, and vanilla extract, then whisk until fully combined.

5. Stir the dry ingredients into the wet ingredients until almost combined.

6. Pour in the hot coffee or hot water and mix until the batter is smooth.

7. Fold in the chocolate chips.

8. Divide the batter evenly among the liners, filling each about two-thirds full.

9. Bake for 18 to 22 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

10. Cool the cupcakes in the pan for 5 minutes, then transfer to a wire rack and cool completely.

11. Beat the softened butter for the frosting until creamy.

12. Add the powdered sugar, cocoa powder, heavy cream, vanilla extract, and salt, then beat until fluffy.

13. Mix in the melted chocolate and beat again until smooth.

14. Pipe or spread the frosting over the cooled cupcakes and serve.