For the chocolate cake, preheat oven to 350˚F. Place flour, sugar, butter, cocoa powder, baking soda and baking powder in the bowl of a standing mixer fitted with a paddle attachment. Mix on slow until all ingredients are combined. Increase speed to medium and continue to mix until mixture is smooth. Stop the mixer and add the melted chocolate. Mix for 1 minute, then, with the machine on, add the hot water, then add the eggs, 1 at a time and waiting until the previous egg is incorporated, then add the buttermilk. Stop the mixer occasionally to scrape down the sides and bottom of the bowl. 

Pour cake batter into a buttered 8-inch cake pan and bake until a cake tester inserted in the center comes out clean, 25 to 30 minutes. Let cool completely.

Carefully halve the chocolate cake horizontally into 2 layers. Scoop half of the ice cream onto 1 cake layer, spreading evenly, then set the remaining cake layer on top. Wrap the cake tightly with plastic wrap, then transfer the ice cream cake to the freezer and let set while preparing the meringue.

For the meringue, whip egg whites until medium stiff peaks form. Add sugar and whip until peaks are stiff and shiny.

Remove the ice cream cake from the freezer, unwrap, and place on a turntable or cake stand. Scoop the meringue onto the cake and frost until covered in a smear pattern. Using a kitchen torch, toast the meringue and serve immediately.