Step 1: Preheat your oven to 175°C (350°F) or 155°C (310°F) for fan-assisted ovens. Thoroughly grease your 23cm springform pan with butter, ensuring you reach all edges and corners. Line the bottom with a circle of baking paper cut to fit precisely.

Step 2: Sift together the flour, baking powder, and salt into a medium bowl. This aerates the dry ingredients and ensures no lumps remain. Set this mixture aside for later incorporation.

Step 3: Separate your eggs carefully, ensuring no yolk contaminates the whites. In a large bowl, whisk the egg yolks using an electric hand mixer on medium-high speed for 2 minutes until they become pale and slightly thickened.

Step 4: Add 2 tablespoons of the sugar to the yolks and continue whisking for approximately 5 minutes. The mixture should become thick, creamy, and form ribbons that drip slowly from the whisk when lifted. This ribbon stage is crucial for the sponge’s texture.

Step 5: Gently fold the sifted flour mixture into the egg yolk mixture using a rubber spatula, making broad, sweeping motions from the bottom up. Add the lemon zest and melted butter, folding just until combined. Be careful not to overmix, which would deflate the batter.

Step 6: In a separate clean, completely grease-free bowl, whisk the egg whites with the cream of tartar using clean beaters. Start at medium speed until foamy, then increase to high speed. Gradually sprinkle in the remaining sugar while whisking continuously.

Step 7: Continue whisking the egg whites until stiff, glossy peaks form. The meringue should stand upright when you lift the whisk and have a smooth, shiny appearance.

Step 8: Fold a large spoonful of meringue into the egg yolk batter to lighten it. Then carefully fold in the remaining meringue in two additions, maintaining as much air as possible.

Step 9: Pour the batter into your prepared springform pan and gently smooth the surface with a spatula. Bake for 12-14 minutes until the sponge springs back lightly when touched but remains quite pale. Avoid overbaking, as this layer should be tender.

Step 10: Remove from the oven and let cool on a wire rack while you prepare the remaining layers. Once cooled, wrap the entire bottom and sides of the springform pan tightly with aluminum foil to create a waterproof seal for the water bath baking.

Step 11: Chop the dark chocolate and butter into small, uniform pieces. Place them in a heatproof bowl set over a saucepan of gently simmering water (double boiler method). Ensure the bottom of the bowl doesn’t touch the water to prevent scorching.

Step 12: Stir occasionally until the chocolate and butter are completely melted and smooth. Remove from heat and set aside to cool for 10 minutes. The mixture should be warm but not hot when you add the eggs.

Step 13: Whisk in the eggs one at a time, ensuring each is fully incorporated before adding the next. The mixture should become glossy and slightly thickened.

Step 14: Stir in the sugar until dissolved and well combined. Sift the flour, baking powder, and salt directly into the chocolate mixture, then fold gently until no flour streaks remain. The batter should be thick and glossy.

Step 15: Pour the chocolate brownie batter over the cooled sponge base in the springform pan, spreading it evenly to the edges. The brownie layer will be quite thick.

Step 16: Ensure your cream cheese is at room temperature for smooth mixing. In a large bowl, beat the cream cheese with the vanilla pudding powder and sugar using an electric mixer until completely smooth and fluffy, about 2-3 minutes.

Step 17: Add the eggs one at a time, beating well after each addition. Scrape down the sides of the bowl to ensure even mixing.

Step 18: Mix in the vanilla extract until evenly distributed throughout the cream cheese mixture.

Step 19: In a separate bowl, whip the heavy cream to soft peaks. Gently fold the whipped cream into the cream cheese mixture in two additions, creating a light, mousse-like texture.

Step 20: Carefully pour and spread the vanilla cream cheese mixture over the chocolate brownie layer, smoothing the top with an offset spatula or the back of a spoon.

Step 21: Reduce the oven temperature to 160°C (320°F) or 140°C (285°F) for fan-assisted ovens. Place the foil-wrapped springform pan inside a larger roasting pan.

Step 22: Create a water bath by pouring hot water into the roasting pan until it reaches halfway up the sides of the springform pan. This gentle cooking method prevents cracks and ensures even baking.

Step 23: Carefully transfer the roasting pan to the oven and bake for 38-41 minutes. The cheesecake should be set around the edges but still have a slight wobble in the center when gently shaken.

Step 24: Turn off the oven and crack the door open slightly. Let the cheesecake cool gradually in the oven for 1 hour. This prevents thermal shock that causes cracking.

Step 25: Remove from the oven and water bath, discard the foil, and let cool completely at room temperature. Once cooled, refrigerate for at least 4 hours or preferably overnight before serving. This allows the layers to set properly and flavors to meld beautifully.