Prepare the Tin and Oven: Preheat your oven to 180°C (160°C fan). Grease and line a 23 x 33cm (9 x 13 inch) baking tray with parchment paper, leaving a little overhang on the sides to make it easier to lift the cake out later.

Combine Dry Ingredients: In a large mixing bowl, or the bowl of a stand mixer, whisk together the plain flour, caster sugar, sifted cocoa powder, bicarbonate of soda, baking powder, and salt. Give it a good mix to ensure everything is evenly distributed.

Combine Wet Ingredients: In a separate medium bowl or jug, whisk the eggs, buttermilk, vegetable oil, and vanilla extract until smooth and fully combined.

Mix the Batter: Pour the wet ingredients into the dry ingredients. Mix on a low speed (or by hand with a whisk) until just combined. Be careful not to overmix – stop as soon as you no longer see streaks of flour.

Add the Coffee: With the mixer still on low, carefully pour in the hot coffee. The batter will become very thin. I find that this is the moment people worry, but trust the process! This liquid batter is what creates that signature moist crumb. Mix for about 30 seconds until the coffee is incorporated.

Bake the Cake: Pour the batter into your prepared baking tray and spread it out evenly. Bake for 25-30 minutes, or until a skewer inserted into the centre of the cake comes out with a few moist crumbs attached, but no wet batter.

Cool Completely: Let the cake cool completely in the tin on a wire rack. This is a vital step as it traps moisture. Don’t be tempted to ice it while it's still warm, as the icing will just melt and slide off.

Make the Icing: While the cake cools, prepare the icing. In a large bowl, beat the softened butter with an electric hand mixer or in a stand mixer until it’s light and fluffy, about 2 minutes.

Finish the Icing: Gradually add the sifted icing sugar and cocoa powder, mixing on low speed until combined. Add the milk and vanilla extract, then increase the speed to medium-high and beat for 2-3 minutes until the icing is smooth, glossy, and spreadable.

Ice the Cake: Once the cake is completely cool, spread the icing evenly over the top using an offset spatula or the back of a spoon. Add your sprinkles or chocolate shavings immediately, before the icing sets. Allow the icing to set for at least 30 minutes before slicing and serving.