Instructions

1. 1
   Pound the digestive biscuits into crumbs with the end of a rolling pin.
2. 2
   Add sufficient melted butter to the crumbs to make the mixture cohesive. Mix well, then press it into the bottom of a 10 inch (25 cm) diameter, 1 inch deep pie dish. Press down firmly with the tip of a spoon to make the base.
3. 3
   Combine the sweetened condensed milk and egg yolk. Stir gently, then mix in the lemon zest and juice to taste—more will be better, but be careful not to add too much or it will spoil the texture. Do not stir too much.
4. 4
   Pour the filling into the pie dish, covering the biscuit layer.
5. 5
   Whip the egg whites until foamy. Gradually beat in the sugar until you get stiff peaks.
6. 6
   Spoon the meringue into the pie dish, sealing around the edges.
7. 7
   Bake in a moderately cool oven (325 °F / 162 °C) for about 45 minutes until the meringue is a light golden brown. The aim is to cook the meringue and partly cook the centre (unlike, say, Baked Alaska, where only the top of the meringue is flash-cooked).
8. 8
   Remove from the oven, allow to cool, and place in the refrigerator for 2 hours to set.
9. 9
   Enjoy.