Chocolate Whoopie Pies with Buttercream and Dark Chocolate Glaze

Method

1. Preheat the oven to 350°F/gas 3. Line two large baking trays with greaseproof paper.
2. Sift together the flour, cocoa powder, baking powder, bicarbonate of soda and a pinch of sea salt into a bowl.
3. Chop the dark chocolate and melt it together with the butter in a heatproof bowl set over a pan of barely simmering water. Stir until smooth, then remove from heat and set aside to cool.
4. In a large bowl, lightly beat the egg. Whisk in the light muscovado sugar, caster sugar and soured cream until well combined. Stir in the melted chocolate and butter mixture.
5. Add the sifted dry ingredients and 5 tablespoons of boiling water. Mix until the batter is smooth. Fold in the white chocolate chips.
6. Spoon 12 even dollops of batter onto each prepared baking sheet, leaving plenty of space between them. Bake on the middle shelf for 10 to 12 minutes.
7. Let the whoopie pies cool on the trays for a few minutes, then transfer them to a wire rack to cool completely.
8. For the buttercream frosting, melt the white chocolate in a heatproof bowl over a pan of simmering water. Stir until smooth, then set aside to cool.
9. Sift the icing sugar into a large bowl. Add the room-temperature butter and vanilla extract, then beat until smooth and light. Stir in the cooled white chocolate until fully incorporated.
10. Fill a large piping bag with the buttercream. Pipe a generous amount onto the flat side of 12 of the whoopie pies. Sandwich them with the remaining 12 cakes to form the pies.
11. To make the glaze, combine all the glaze ingredients in a heatproof bowl over a pan of simmering water. Stir until smooth and slightly thickened. Remove from heat and let cool slightly. Spoon the glaze over the whoopie pies, decorate with sprinkles if desired, and let set before serving.