Prepare a pot with 1” of water and bring to a simmer.
Mix egg whites with sugar in a heatproof bowl and place above the pot of simmering water and constantly stir until the sugar is fully dissolved.
Using a stand mixer or hand mixer, whisk the egg mixture until glossy and peaks. Making sure the mixture is not too hot.
Lower the speed of the mixer and slowly add cube of butter in making sure to let the butter incorporate before you add the next piece.
Meanwhile, melt chocolate in a microwave or double boiler.
Add melted chocolate into buttercream and whisk till combine.
To make the drip topping, putt chocolate and cream together in a heatproof bowl and melt in a microwave, stir till combine. It should be slightly runny, if it's too firm, add more cream. Keep warm.
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