Mix the egg yolk and condensed milk add the lemon juice and whisk vigorously until it thickens. (Don’t overmix). Pour mixture over the biscuit base. Now make a meringue by beating the egg whites to almost stiff and then add the granulated sugar (spoon-by-spoon). Cover the pie with the meringue. Bake in a pre-heated oven at 160ºC for about 8 to 12 minutes or until the meringue has a nice golden colour. Cool down and serve. This pie will keep in the fridge for up to two days.