Prepare the base:

• Crush the digestive biscuits into fine crumbs using a food processor or by placing them in a sealed bag and crushing with a rolling pin.

• In a bowl, mix the biscuit crumbs with the melted butter until the mixture resembles wet sand.

• Press the mixture into the base of a springform tin (around 20cm/8 inches), and refrigerate for 30 minutes to firm up.

Prepare the filling:

• In a large bowl, beat the cream cheese and icing sugar together until smooth and creamy.

• In another bowl, whip the double cream until it holds soft peaks.

• Zest the lemon and lime, then add the zest and juice of both to the cream cheese mixture. Stir gently to combine.

• Dissolve the gelatin in a little warm water, following the packet instructions (or prepare agar-agar as directed for a vegetarian version). Let it cool slightly before adding it to the cream cheese mixture. Stir until evenly incorporated.

• Gently fold the whipped cream into the cream cheese mixture until fully combined.

Assemble the cheesecake:

• Spoon the filling onto the chilled biscuit base, smoothing the top with a spatula.

• Refrigerate the cheesecake for at least 4 hours, or ideally overnight, to allow it to set properly.

Serve:

• Once set, carefully remove the cheesecake from the springform tin.

• Garnish with extra citrus zest or thin slices of lemon and lime if desired before serving.