1. Preheat the oven to 350°F and lightly grease a heart-shaped muffin pan or line a standard muffin tin and shape the liners as needed.

2. In a large mixing bowl, whisk together the flour, cocoa powder, sugar, baking powder, baking soda, and salt.

3. Add the eggs, buttermilk, vegetable oil, and vanilla extract, then mix until the batter is smooth.

4. Slowly pour in the hot coffee or hot water and stir until fully combined.

5. Divide the batter evenly into the prepared pan, filling each cavity about two-thirds full.

6. Bake for 14 to 18 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

7. Let the cupcakes cool in the pan for 10 minutes, then transfer them to a wire rack and cool completely.

8. To make the frosting, beat the butter until creamy, then mix in the cocoa powder, powdered sugar, vanilla extract, and heavy cream until fluffy.

9. Transfer the frosting to a piping bag fitted with a star tip and pipe a heart-shaped swirl on top of each cupcake.

10. Finish with pink and red sprinkles in the center and serve.