Instructions:
- Preheat oven to 325°F (160°C). Boil kettle water for the water bath. Wrap the exterior bottom and sides of the 9-inch springform pan tightly in two layers of heavy-duty foil.
- Combine crushed biscuits, melted butter, and 2 tbsp sugar. Press firmly and evenly into the bottom of the prepared pan. Blind Bake the crust for 10 minutes. Remove and let cool slightly. Reduce oven temperature to 300°F (150°C).
- Gently toss the blueberries with 1 tbsp sugar and 1 tsp lemon juice. Set aside to macerate while preparing the filling. (Optionally, simmer half the berries to create a thick syrup for swirling).
- Beat the softened cream cheese and 250g sugar on medium speed until perfectly smooth, scraping down the bowl constantly (about 3 minutes). Ensure no lumps remain.
- Beat in the sour cream/crème fraîche, lemon zest, juice, and vanilla until just combined. Add the flour/cornstarch and mix on low speed.
- Add the eggs and extra yolks one at a time, mixing only until each is incorporated. STOP MIXING AS SOON AS THE LAST YOLK IS BLENDED to avoid incorporating excess air.
- Pour about 2/3rds of the filling over the cooled crust. Spoon dollops of the macerated berries over the batter. Pour the remaining filling on top.
- Gently swirl the berries through the top layer using a butter knife. Place the foil-wrapped springform pan inside a large roasting pan.
- Carefully place the roasting pan in the oven. Pour the boiling water into the roasting pan until it reaches about halfway up the side of the springform pan (the water bath).
- Bake at 300°F (150°C) for 65–75 minutes. The edges should look set, but the centre 2 inches should still wobble slightly.
- Turn the oven off. Prop the oven door open slightly (using a wooden spoon) and allow the cheesecake to cool gradually inside the oven for 1 hour.
- Remove from the water bath, unwrap the foil, and let it cool completely on a wire rack at room temperature. Cover loosely and chill in the refrigerator for a minimum of 6 hours, preferably overnight, before slicing.