Use a grinder to crumble biscuits into fine crumbs. Add sugar and butter. If it feels too dry, add a tbsp of milk.
Grease pie plate. Put mixture and press down evenly on base and sides. Allow to set firmly in freezer.
Take all the ingredients of the filling and heat in a heavy saucepan. Stir continuously. When the mixture thickens, take off from the fire and let it cool.
Spread mixture on to the crust evenly and chill to set.
Over a bowl of chilled water, beat the cream with a hand beater to incorporate air. Beat in small, sharp, upward strokes. Add sugar and gently mix till cream is thick, light and fluffy. Spread onto filling to cover and form peaks all over.