Gently melt the butter in a small pan
over a low heat. Place the digestives in
a plastic bag and crush to fine crumbs
using a rolling pin; you can also do this in
a food processor. Tip them into the pan
with the melted butter, stir to coat, then
transfer to a 20cm springform cake tin
(9cm deep). Using the back of a spoon,
press them into the base, making sure
you seal the edges. Place in the fridge
while you prepare the next stage.
If using leaf gelatine, place in a bowl,
cover with cold water, soak for 5 mins,
then drain. Pour 3 tbsp boiling water over
the soaked gelatine and stir to dissolve.
If using a sachet, see Know-how, below.
Place the crème fraîche in a small pan
with the muscovado sugars and a pinch
of sea salt, then gently heat, stirring
constantly with a wooden spoon until
the mixture liquefies and the sugar has
dissolved. Give the mixture a quick whisk
to get rid of any lumps. It should be warm,
roughly the same temperature as the
gelatine solution. Stir the gelatine and
vanilla extract into the crème fraîche
mixture, transfer to a bowl and cool.
Place the ricotta in a food processor
and whizz until smooth, then add the
crème fraîche mixture and whizz again.
Pour this on top of the cheesecake base.
Cover with cling film and chill overnight.
Run a knife around the sides of the tin,
then undo the clip and remove it. Transfer
to a plate or leave the cheesecake on the
base for ease of serving. Pile the fudge
flakes in the centre and dust with icing
sugar. Cover and chill until required.