Preheat oven to 375 degrees. Lightly butter or line 16 muffin cups with paper liners.

In a small bowl, stir the boiling hot water and the cocoa powder until smooth. Let cool to room temperature.

In another bowl, whisk together the flour, baking powder, and salt.

Then, in the bowl of your electric mixer, or with a hand mixer, beat the butter and sugar until light and fluffy. Add the eggs one at a time, beating until smooth. Scrape down the sides of the bowl as needed. Beat in the vanilla extract.

Add the flour mixture and beat only until incorporated. Then slowly and carefully add the cooled cocoa mixture and stir until smooth.

Fill each muffin cup about two-thirds full with batter and bake for about 18-20 minutes or until risen, springy to the touch, and a toothpick inserted into a cupcake comes out clean. Remove from oven and place on a wire rack to cool.

In a stand mixer fitted with the whisk attachment, beat the butter at medium-high speed until smooth, about 20 seconds. If using a vanilla bean, using a paring knife, scrape seeds from vanilla bean into butter. If using vanilla bean paste, add it instead. Beat mixture at medium-high speed to combine, about 15 seconds.

Add powdered sugar and salt; beat at medium-low speed until most of the sugar is moistened, about 1 minute. Scrape down the bowl and beat at medium speed until mixture is fully incorporated about 30 seconds; scrape bowl, add vanilla and heavy cream, and beat at medium speed until incorporated about 20 seconds, then increase speed to medium-high and beat until light and fluffy, about 4 minutes, scraping down bowl once or twice.

Once the cupcakes have completely cooled, top with this frosting. You can either spread the frosting on the cupcakes with a small spatula or if piping, use a large Wilton 1M open star tip to make lovely swirls.