Preheat the oven to 325°F (165°C). Lightly grease the inside of a 9-inch (23 cm) springform pan. Wrap the outside bottom and sides securely with two layers of heavy-duty aluminum foil to help keep water from entering during the water bath.

Combine the vanilla wafer crumbs, melted butter, and 2 tablespoons (25 g) granulated sugar. Stir until the crumbs are evenly moistened and resemble damp sand. Press firmly across the bottom of the prepared pan.

Bake for 10 minutes, until the crust looks set and smells lightly toasted. Remove it from the oven and let it cool while preparing the filling. Keep the oven at 325°F (165°C).

Beat the softened cream cheese on medium-low speed until smooth, scraping down the bowl as needed. Add 1 cup (200 g) granulated sugar and mix until smooth and creamy. Avoid whipping in unnecessary air.

Mix in the sour cream and vanilla extract on low speed until evenly incorporated. The batter should be thick, smooth, and free of visible cream cheese lumps.

Add the eggs one at a time on low speed, mixing only until each egg disappears into the batter before adding the next. Scrape down the bowl once as needed. The finished batter should be creamy and pourable rather than fluffy.

Gently fold the chopped pieces from 4 Christmas Tree Cakes into the batter with a rubber spatula. Use only a few strokes so the pieces remain distinct instead of breaking down completely.

Pour the filling over the crust and smooth the top. Set the wrapped springform pan inside a large roasting pan. Carefully pour hot water into the roasting pan until it reaches about halfway up the outside of the springform pan.

Bake at 325°F (165°C) for 65 to 75 minutes. The outer 2 to 3 inches should look set, while the center should still move as one soft, cohesive area when the pan is gently nudged. It should not look liquid or ripple loosely.

Turn off the oven, crack the door open, and leave the cheesecake inside for 1 hour. Carefully remove it from the water bath and remove the foil. Cool on a rack at room temperature for another 1 hour.

Cover the cheesecake once it is cool and refrigerate for at least 6 hours, preferably overnight. The center should become fully chilled and firm enough to hold a clean slice.

Place the chopped white chocolate in a heatproof bowl. Heat the heavy cream just until steaming, then pour it over the chocolate. Let stand for 2 minutes before stirring gently until smooth and glossy. If small pieces remain, warm the mixture very briefly and stir again. Let it cool until slightly thickened but still pourable.

Remove the chilled cheesecake from the springform pan: Spread or pour the white chocolate topping over the surface. Pipe thin zigzags of red decorating icing across the top and sprinkle with green sanding sugar.

If desired, arrange the halved Christmas Tree Cake on top just before serving. Chill briefly if needed to set the topping, then cut the cheesecake into 12 slices with a sharp knife, wiping the blade clean between cuts.