Photograph: Martin Poole
Whiz the shortbread in a food processor to fine crumbs. Transfer to a bowl and stir in the melted butter. Line a 12-hole muffin tin with paper cases and divide the mixture among them. Press down with the back of a spoon. Chill.
Soak the gelatine leaves in a shallow bowl of cold water for 5 minutes, then remove and place in a small pan with 3 tablespoons of water. Stir over a very low heat until the gelatine has dissolved.
Put the sugar and cream cheese into a bowl and whisk until combined. Add the double cream, lemon zest and juice, condensed milk and dissolved gelatine and whisk with an electric hand whisk until smooth and slightly thickened. Divide the mixture equally among the paper cases, filling them to the top.
Pour the melted chocolate into a disposable piping bag and snip off the tip. Pipe a spiral on to the top of each cheesecake then, using a cocktail stick, draw lines from the centre of each cheesecake out to the edge to make it look like a spider's web. Chill for 3-4 hours until set. Remove from the fridge 30 minutes before serving.
Get ahead: make the day before. They also freeze well.