4 gelatine leaves (I used Supercook), cut into wide strips (or 1 x 11g sachet, see Know-how, below)
400g creme fraÃ®che
100g light muscovado sugar
50g dark muscovado sugar
1 tsp vanilla extract
50g fudge, finely sliced
icing sugar, for dusting
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 creme fraÃ®che 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 creme fraÃ®che mixture, transfer to a bowl and cool.
Place the ricotta in a food processor and whizz until smooth, then add the creme fraÃ®che 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.