Crush biscuits and mix with the melted butter and sugar.
Press into 7" sandwich/flan tin
Bake at Gas Mark 2/ 150 degrees for 8 minutes and leave to cool.
Mix together the cream, condensed milk and the zest into soft peaks
Slowly beat in the lemon juice.
Spread topping over the base and chill until the topping has set.
Tip: This can also be frozen-Defrost at room temperature.