Chocolate caramel dessert thingy

Is it a pie? (Not really, no pastry.) Is it a cake? (Not baked, no crumb, probably not.) Is it a torte, tart or pudding? (Who the hell knows? But it's a dessert, and that's what counts.)

Last Friday I went round to my friend Rachel's place for dinner. What I'd forgotten, when I said I'd bring dessert, was that I had 28 student papers to mark that afternoon, that I desperately needed to wash my hair and that I hate making desserts. Lack of time, lack of creativity and lack of suggestions from other friends (no, Yo-Han, "go to M&S" does not count) resulted in the following...

This recipe, as usual without photos, brought to you by the letters W, T and F, the number pi (not pie, see above for explanation), my need for an express dessert to take to dinner that doesn't involve a visit to M&S, and the fact that my digital camera is still broken.

Base
1/2 packet digestive biscuits
125g butter

Melt butter, meanwhile squash biscuits, combine and mix well. Press into base of 20cm springform tin.

Caramel layer
225g (1 scant cup) sugar
60g butter
1/2 cup cream

Method 1: Place sugar in saucepan over medium heat, shaking occasionally to distribute heat as sugar melts. Continue to cook until golden brown and bubbling. Whisk in butter and cream (be careful in case it boils over) and continue to stir vigorously and heat until the mixture is a uniform texture.
[Alternatively, Method 2: if in a hurry, start sugar over too high a heat so it browns before it's all dissolved; swear and stir, hoping it won't be too lumpy; whisk in cream and butter before it burns; swear some more as the mixture seizes; continue to stir, heat and swear continuously under your breath while you become later and later as you wait for the giant lumps of seized caramel to dissolve; finally give up and leave some crunchy bits in. Method 1 is definitely more highly recommended.]
Pour caramel mixture over crumb base.

[Optional extra step: if now running so late you're in danger of not being able to get there at all, postpone next steps and take remaining ingredients with you in carrier bag to friend's house so you can complete it there. Alternatively, if you're actually a vaguely organised and grown-up person with time management skills, you can skip this step, cool your caramel in the fridge like a normal person and then go on.]

Chocolate layer
250g dark (70%) chocolate
475ml cream (this seems like an odd amount til you realise cream comes in 300ml pots)

Whack chocolate and about half of cream in microwave til melted (1:30-2:00 depending on your microwave). Mix til smooth and stir in rest of cream thoroughly. Pour over set caramel layer and jiggle until surface is adequately smooth.

Chill in fridge at least a couple of hours if you can; if you're too disorganised even for that, chill until you hope it's set enough to cut, or until you think dinner guests are too drunk to notice; slice and serve.