Step 1

Grease and line a 32cm x 22cm baking tin with paper, allowing it to come up the sides and overhang slightly.

Step 2

In a food processor, blitz biscuits into a fine crumb. Stir through melted butter. Tip into prepared tin and use a large spoon or the base of a flat glass to press into an even layer. Refrigerate to set.

Step 3

Sprinkle gelatine over 1 tbsp water in a small bowl. Leave for 3-4 minutes to bloom, then place in a small saucepan with a little simmering water in the base. Stir until gelatine dissolves and mixture is smooth. Remove from saucepan.

Step 4

In the bowl of a stand mixer or using hand-held beaters, whisk condensed milk with lemon juice and zest. Add gelatine mixture and cream, and beat until starting to thicken. Pour over biscuit base in tin and smooth the top.

Step 5

Refrigerate for at least 4 hours to set. Use overhanging paper to gently ease and lift slice out of tin. Cut into squares.