You’ll need to make two consecutive batches of the marshmallow frosting to cover all 24 cupcakes with a high mound of frosting, as shown in the photographs. Use caster sugar in the frosting recipe, which is quick melting and will yield a smooth result.
Make the cupcakes: Preheat oven to 350°F. Line two muffin tins with parchment cupcake papers and set aside. Sift together cocoa, flour, sugar, baking soda, baking powder and salt into a large bowl. Add eggs, water, heavy cream, oil and vanilla. Mix with a hand held mixer until smooth. Divide batter among muffin cups, filling each half full. Bake 15-20 minutes. Let cool completely on a cooling rack before frosting.
Make the frosting: Heat a saucepan of water over medium heat until simmering; reduce heat until water barely simmers. In a large heatproof bowl, combine the sugar, water, egg whites, and cream of tartar. Beat with a handheld mixer until foamy, about 1 minute. Set the bowl over the pan of simmering water and beat on high speed until frosting forms stiff peaks, about 12 minutes. For accuracy, frosting should register 160°F on a candy thermometer and no granules of sugar detected when you rub a bit of frosting between your fingers. Beat in vanilla extract and whip about 2 additional minutes. (Make a second batch of frosting to cover all 24 cupcakes with a tall amount of frosting.)
Transfer the frosting to a large pastry bag fitted with a 1/2-inch plain pastry tip. Pipe a mound of frosting into a high cone shape. Transfer cupcakes to a wax paper-lined baking sheet.
Make the chocolate coating: Combine ruby chocolate and oil in a medium heat-proof bowl set over a pan of barely simmering water. Stir until melted and smooth. Transfer to a tall cup or glass measure. Let cool 10 minutes.
Hold a cupcake by its bottom and quickly dip in the chocolate. Immediately turn the cupcake upright and place on the baking sheet. Repeat with remaining cupcakes. Return cupcakes to the wax paper-lined baking sheet. Allow the cupcakes to stand at room temperature 5 minutes and then sprinkle on decors. Transfer to the refrigerator and chill. Cupcakes are ready to serve when the chocolate coating has set and has a matte appearance.
Keyword edible flowers, hi hat cupcakes, ruby chocolate