Preheat the oven to 180°C/350°F/Gas 4.
Combine the almonds and panettone in a food processor and whizz until it forms a fine meal. Rub an 18 cm spring-clip cake tin generously with 15 g of the butter, and sprinkle with some of this mixture. Roll the mixture around to form an even coating, and then invert the cake tin to shake out excess nuts and breadcrumbs.
Melt the chocolate with 2 tbsp water in a double boiler or microwave. Whilst this is melting, cream the remaining butter and the sugar in the food processor. Add the eggs, the scraped-out vanilla seeds, chocolate, remaining nut and panettone mix and the mascarpone. Whizz until just incorporated, no more. Pour and scrape into the prepared cake tin, and bake for about 40 minutes. The cake should be just about set: cracks will appear about 2 cm in from the rim and when they have spread all around the cake in a circle, this is a pretty certain indication it is done.
Remove from the oven and leave to sit for 20 minutes before unmoulding. It is best served warm when it may be a little runny in the middle. This is not a problem; remember how much you liked raw cake mix as a kid – fight with your siblings over the bowl!