1. Make the Chocolate Sponge

Start by preheating your oven to 170°C (340°F). Grease a 20 x 3.5 x 31.5cm cake tin and line it with baking parchment. The parchment will help prevent the cake from sticking to the pan, making it easier to remove once cooled.

Next, in a jug, combine the milk, vinegar, vanilla extract, and oil. Let this mixture sit for 5 minutes to allow it to curdle slightly. This creates a buttermilk substitute, which helps give the sponge a soft, light texture.

In a large mixing bowl, sift together the self-raising flour, baking powder, cocoa powder, cornflour, caster sugar, and salt. Sifting helps remove lumps and ensures an even distribution of dry ingredients.

Once sifted, pour the wet milk mixture into the dry ingredients and whisk them together until smooth. Be careful not to overmix the batter, as this can result in a dense sponge.

Pour the batter into the prepared tin, smoothing the top with a spatula. Bake for 18–20 minutes, or until the cake is springy to the touch. If you insert a skewer into the center, it should come out clean. Let the sponge cool in the tin for 10 minutes, then transfer it to a wire rack to cool completely. Once the sponge has cooled, peel away the parchment and slice the sponge into 12 equal rectangles.

2. Prepare the Espresso Mixture

In a separate bowl, mix the instant espresso powder with the hot water. Stir until the espresso powder is completely dissolved. If you want a more adult twist, replace 150ml of the water with dark rum, whiskey, or Irish cream liqueur. The alcohol will complement the rich espresso flavor and add depth to the overall taste of the dessert.

Allow the espresso mixture to cool to room temperature before using it to soak the sponge layers.

3. Make the Mascarpone Cream

To make the mascarpone cream, combine the mascarpone, double cream, and icing sugar in a large bowl. Using an electric mixer or a whisk, beat the mixture until it thickens into a smooth, velvety cream. This will take about 2–3 minutes, so be patient. The cream should be thick enough to hold its shape but still smooth. If it becomes too thick, you can loosen it with a tablespoon of milk.

4. Assemble the Millionaire’s Tiramisu

Now that all the components are ready, it’s time to assemble the tiramisu. You’ll need a deep dish or tray, about 30cm wide and 5cm deep, for layering the ingredients.

Start by dipping each piece of chocolate sponge into the cooled espresso mixture for about 5 seconds, ensuring it’s soaked but not falling apart. Arrange six pieces of sponge in a single layer at the bottom of the dish.

Next, spread half of the mascarpone cream evenly over the sponge. Sprinkle half of the crumbled shortbread biscuits on top, followed by half of the salted caramel. Repeat the same layering process, this time using the remaining sponge, mascarpone cream, shortbread crumbs, and caramel.

Once you’ve finished layering, sift the cocoa powder over the top of the tiramisu using a fine sieve. This creates a beautiful finish and adds a rich chocolate flavor that complements the other layers.

5. Let the Tiramisu Set

Now, cover the dish with plastic wrap and refrigerate the tiramisu for at least 12 hours, or preferably overnight. This allows the flavors to meld together, and the dessert will have a firmer texture, making it easier to cut into neat slices.