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1
For the cupcakes:
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Preheat oven to 350 F. Grease a standard size 12-count muffin tin or line with muffin liners. Set aside.
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3
In a large bowl, mix together sugar, flour, cocoa powder, baking powder, baking soda and salt. Crack in the egg, spoon in the sour cream, and pour in the oil and the vanilla. Mix with a wooden spoon until just combined.
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Pour in the boiling water, and slowly mix until smooth. Divide batter evenly among prepared muffin cups, filling each about halfway full.
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Transfer muffin tin to the oven and bake for 15 to 18 minutes. Remove it from the oven and transfer muffin tin to a wire rack and let cupcakes cool completely.
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6
For the frosting:
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In a large heatproof bowl, combine sugar and egg whites. Using a handheld electric mixer, beat on high speed until foamy for one minute. Set bowl over a pan of barely simmering water. Beat on high speed until frosting forms stiff peaks, about 10 minutes. Remove from heat, stir in vanilla and water, and beat for another two minutes until frosting thickens.
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8
Using a small paring knife, cut off the top of the cupcake in the shape of a cone. Flip the top over and cut off the pointy part of the cone and set aside. Fill the cavity with a teaspoon of frosting. Replace the top.
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Transfer remaining frosting into a pastry bag fitted with a small plain pastry tip. Set aside.
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10
For the ganache:
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Place the chocolate, heavy cream and corn syrup in a medium heatproof bowl over a pot of simmering water. Stir the mixture using a wooden spoon until melted and smooth, about 5 minutes.
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Grab each cupcake from the bottom, dip the top of the cupcake in the ganache to coat it and let excess drip off. Set on a piece of parchment paper. Let cupcakes stand at room temperature for 5 minutes to set the ganache.
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13
Pipe remaining frosting in swirls across the centre of each cupcake.
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14
Best served on the day the marshmallow frosting is made.
