1. Preheat the oven to 350°F and line a muffin pan with cupcake liners. Add a marble or small foil ball beside each liner to help create a heart shape.

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

3. In a large bowl, beat the eggs, granulated sugar, and brown sugar until smooth. Mix in the oil, vanilla extract, and buttermilk.

4. Add the dry ingredients to the wet ingredients and stir just until combined.

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

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

7. Bake for 16 to 20 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

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

9. To make the frosting, beat the butter until creamy. Add powdered sugar, cocoa powder, cream or milk, vanilla extract, and salt. Beat until light and fluffy.

10. Frost the cooled cupcakes and decorate with heart sprinkles or chocolate shavings.