To begin, preheat your oven to 180°C (160°C fan). Line two baking trays with parchment paper. Lightly grease the paper to prevent sticking and ensure easy release once baked.

In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy, about 3 to 4 minutes. This creates the base structure for the cakes, so take time to incorporate enough air.

Crack in the egg and add the vanilla extract. Beat until well combined. Scrape down the sides of the bowl to ensure even mixing before proceeding.

In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt. Sifting the cocoa ensures no lumps and a smoother batter.

Alternate adding the dry mix and milk into the creamed mixture in three parts, starting and ending with the dry. Stir gently after each addition. Avoid overmixing to keep the cakes tender.

Use a tablespoon or piping bag to drop 16 evenly sized rounds onto the trays, leaving space for spreading. Bake for 10 to 12 minutes or until the tops spring back lightly when touched. Allow to cool completely on a wire rack.

While the cakes cool, beat together the butter and shortening until smooth. Add icing sugar gradually, then stir in vanilla and milk. Beat on high for 3 minutes until the filling is light and fluffy.

Pair the cake halves by size. Spoon or pipe a generous dollop of filling onto the flat side of one cake, then gently press a matching cake on top. Avoid pressing too hard to maintain their shape.

Place assembled Whoopie Pies in the fridge for 20 minutes to allow the filling to firm up slightly. This makes them neater to eat and enhances texture contrast.

Serve at room temperature for the best flavour and texture. They pair beautifully with a glass of milk or cup of coffee. For a festive twist, roll the edges in sprinkles or crushed nuts just before serving.