Whisk the Dry Ingredients: In a medium saucepan, thoroughly whisk together the cocoa powder, caster sugar, cornflour, and salt until there are no lumps and the mixture looks uniformly pale brown. This initial step prevents clumping later on.

Combine Liquids and Temper Eggs: In a separate bowl, whisk together the semi-skimmed milk, full-fat milk, and egg yolks until well combined and a pale yellow colour. Gradually pour about half of this liquid mixture into the dry ingredients in the saucepan, whisking constantly until smooth. This creates a thick, chocolatey paste.

Cook the Pudding Base: Place the saucepan over a medium heat. Gradually whisk in the remaining milk and egg yolk mixture. Continue to whisk constantly, scraping the bottom and sides of the pan, for about 8-12 minutes. The mixture will slowly thicken, transforming from a thin liquid to a visibly glossy, bubbling pudding. You'll notice the sound of gentle bubbling and the texture will be noticeably thicker, coating the back of a spoon.

Melt in Chocolate and Butter: Once the pudding has thickened to your desired consistency, remove it from the heat. Add the finely chopped dark chocolate and the cubed unsalted butter. Stir gently until the chocolate has completely melted and the butter is fully incorporated, creating a rich, dark brown, shiny mixture with a truly luxurious aroma.

Incorporate Protein and Vanilla: Sprinkle the unflavoured protein powder over the warm pudding and whisk vigorously until it's completely dissolved and smooth. Then, stir in the vanilla extract. The pudding should remain smooth and retain its rich chocolate colour, perhaps deepening slightly. This is where the "high protein" magic happens! I've been making this for over 3 years, and this method for adding protein powder ensures a silky finish every time.

Chill and Serve: Pour the hot pudding into individual serving bowls or a large heatproof dish. For a smooth top, gently press a piece of cling film directly onto the surface of the pudding to prevent a skin from forming. Allow it to cool at room temperature for about 30 minutes, then transfer to the refrigerator to chill for at least 2-3 hours, or preferably overnight. The pudding will firm up further and deepen in flavour as it cools. When ready, it should be cold, thick, and utterly creamy.