Directions
<ol class="no-list-style"><li class="MethodStepper"><h4 class="step-title">Step 1</h4>Preheat your oven to 160°C (140°C fan/325°F). Grease the sides of your springform pan and line the base with baking parchment. Wrap the outside of the pan with two layers of heavy-duty aluminum foil, ensuring it comes at least halfway up the sides (this prevents water from seeping in during baking).</li><li class="MethodStepper"><h4 class="step-title">Step 2</h4>For the base, blitz the chocolate biscuits in a food processor until they form fine crumbs. Mix with the melted butter and cocoa powder until completely combined - the mixture should resemble wet sand and hold together when pressed between your fingers. Press firmly into the base of your prepared tin, creating an even layer. Use the flat bottom of a glass to compact it thoroughly. Chill in the refrigerator while preparing the filling.</li><li class="MethodStepper"><h4 class="step-title">Step 3</h4>Melt both chocolates separately in heatproof bowls over pans of barely simmering water, making sure the bowls don't touch the water (or microwave in 30-second bursts, stirring between each). Allow to cool slightly but remain fluid.</li><li class="MethodStepper"><h4 class="step-title">Step 4</h4>In a large bowl, beat the cream cheese with an electric mixer until completely smooth with no lumps - this is crucial for a silky cheesecake. Gradually add the caster sugar and continue beating until well incorporated and slightly fluffy. The sugar crystals help create tiny air pockets for a lighter texture.</li><li class="MethodStepper"><h4 class="step-title">Step 5</h4>Add the eggs one at a time, beating well after each addition but avoiding overbeating. Scrape down the sides of the bowl frequently to ensure everything is evenly mixed. Overbeating after adding eggs can incorporate too much air, potentially causing cracks.</li><li class="MethodStepper"><h4 class="step-title">Step 6</h4>Fold in the sour cream and vanilla extract with a spatula until just combined. Divide the mixture equally between two bowls. Fold the melted dark chocolate into one bowl and the melted milk chocolate into the other, creating two distinct chocolate mixtures.</li><li class="MethodStepper"><h4 class="step-title">Step 7</h4>Pour the dark chocolate mixture over the chilled base, spreading it evenly. Then carefully spoon the milk chocolate mixture on top. Use a skewer or knife to create gentle swirls between the two chocolate layers if desired, being careful not to overdo it.</li><li class="MethodStepper"><h4 class="step-title">Step 8</h4>Place the springform pan in a large roasting tin. Pour in hot (not boiling) water until it reaches halfway up the sides of the cheesecake pan. This water bath provides gentle, even heat and humidity to prevent cracking.</li><li class="MethodStepper"><h4 class="step-title">Step 9</h4>Bake for 1 hour and 15 minutes, or until the edges are set but the center still has a slight wobble when gently shaken. The cheesecake will continue to set as it cools. Turn off the oven, leave the door slightly ajar, and let the cheesecake cool in the oven for 1 hour - this gradual cooling prevents dramatic temperature changes that can cause cracks.</li><li class="MethodStepper"><h4 class="step-title">Step 10</h4>Remove from the oven and water bath, peel off the foil, and allow to cool completely at room temperature. Once cooled, refrigerate for at least 4 hours or preferably overnight to set fully.</li><li class="MethodStepper"><h4 class="step-title">Step 11</h4>For the ganache topping, place the chopped dark chocolate in a heatproof bowl. Heat the double cream in a small saucepan until it just begins to simmer (don't let it boil). Pour the hot cream over the chocolate and let it sit for 2 minutes before gently stirring until smooth. Add the butter and stir until melted and incorporated, creating a glossy finish.</li><li class="MethodStepper"><h4 class="step-title">Step 12</h4>Allow the ganache to cool for about 10 minutes until slightly thickened but still pourable. Remove the cheesecake from the refrigerator, run a thin knife around the edge to loosen it, then release the springform. Pour the ganache over the top, tilting the cheesecake to ensure even coverage, letting some drip decoratively down the sides.</li><li class="MethodStepper"><h4 class="step-title">Step 13</h4>Return to the refrigerator for at least 30 minutes to set the ganache. Before serving, decorate with chocolate curls, fresh raspberries if using, and a light dusting of cocoa powder. For the cleanest slices, dip your knife in hot water and wipe dry between cuts. Serve chilled for the perfect texture.</li></ol>