Delia Smith's Truffle Torte, something I've been making occasionally over many years. This year I made 2/3 of the truffle mixture, and set it in a 8" diameter springform tin, on a crumb base made using half digestive biscuits and half crisp Amaretti, crushed to fine crumbs and mixed with half their weight of melted butter. I decorated the top with chocolate flutes, getting them to stick to the top of the truffle mix by melting the flat bottoms with the back of a spoon heated in a gas flame. I then dusted with cocoa and icing sugar.
Delia doesn't warn you about this, but it is very crumbly and difficult to cut while really cold, and needs about 30 minutes out of the fridge to soften up before serving. This makes it a nicer texture for eating, too. I forgot to do this, of course, and really struggled to get the first slice out. This is a really rich dessert, and can only be eaten in small slices, but it really allows the true flavour of the chocolate you've chosen to shine through, so needs to be made with a good quality chocolate that you enjoy eating.