Preheat the oven to 110°C and line a tray with baking paper.
Whisk egg whites in a clean bowl until soft peaks form.
Add 300g of sugar and whisk until smooth, glossy, and stiff.
Mix in the cornflour and vinegar on low speed until very stiff.
Pipe a Christmas tree shape with a trunk onto the baking tray.
Fill the shape, smooth the top, and pipe a raised edge with baubles.
Bake for 90 to 120 minutes until firm, then cool completely.
Boil remaining sugar and 150ml water with spices and peels until syrupy.
Stir in blackberries and cool the syrup completely.
Whisk cream and vanilla to soft peaks, then stir in crème de cassis.
Assemble by spreading cream on the meringue and spooning over fruit syrup.