Preheat the oven to 350 degrees F and line one 12-cup standard muffin tin with paper cupcake liners.
In a large bowl, combine the butter, cocoa powder and chocolate. Pour the boiling water over and let stand 5 minutes. Whisk until smooth, and then whisk in the sugar, vanilla and eggs. Whisk in the flour, salt, baking powder and baking soda until just combined. Fold in the walnuts and chocolate chips. Divide the batter among the prepared liners so they are about three-quarters full.
Bake until a toothpick inserted into the center comes out with moist crumbs, 22 to 24 minutes. Cool in the tins 5 minutes, and then cool completely on a wire rack.
While the cupcakes bake and cool, scoop 12 small scoops of ice cream onto a large plate or baking sheet and place in the freezer until hard.
To assemble, scoop off a small piece of the cupcake to make a concave top, and then top each cupcake with a scoop of ice cream. Drizzle the ice cream with hot fudge, and top with some sprinkles and a cherry.