Make the chocolate cakes: Preheat oven to 180C/ 350F and line two baking sheets with parchment paper, or use a whoopie pie tray.

Melt the chocolate and set aside to cool.

Using a stand mixer with the paddle attachment, beat together the butter, muscovado sugar and caster sugar until light and fluffy. Alternatively, in a large mixing bowl, by hand or with an electric hand whisk.

Add the egg to the creamed mixture and beat well, then mix in the melted chocolate and soured cream.

In a separate bowl, sift the flour, cocoa powder and baking powder together, and then gently fold the flour mixture into the cake batter until combined.

If adding chocolate chips, add these to the batter now.

Use an ice cream scoop to divide the batter into equal amounts, about 1 to 1.5 tablespoons on the baking sheets, and allow enough room for the cake cookies to spread as they bake.

Bake for 10-12 minutes or until an inserted skewer comes out clean. Allow to completely cool on a wire rack.

Make the filling: Add the butter, cream cheese, icing sugar and peppermint extract into a large bowl and beat with a stand or hand mixer, until smooth and creamy. Be careful not to overbeat the frosting as the cream cheese will slacken and maybe runny when piping.

Assemble the whoopie pies: On the flat side of half the cooled cake cookies spread or pipe the mint frosting over the flat side, then top with an unfrosted cake cookie. Push the top down slightly so the frosting spreads to the edge.