Make the base by mixing the melted butter with the crushed biscuits. Grease a 20 cm diameter tin with butter and press the biscuit mixture over the base. Leave to cool in the fridge until it hardens.
Mix together the walnut drink, lemon juice, 3 whole eggs and 2 yolks. Add the sugar and sifted flour and stir to make a smooth paste. Add the zest of ½ lemon.
Pour over the biscuit base and bake for about 35 minutes at 170 °C.
When it’s cooked, leave to cool for a few hours in the fridge. Top with whipped cream or, if you prefer, make a meringue by mixing the 2 leftover egg whites with sugar and beat to stiff peaks.