Preheat the oven to 350°F (180°C) without the fan going, just regular bake. Grease a 9-inch pie pan with melted butter or baking spray.

Place the crackers in the bowl of a food processor and blitz until they have the consistency of sand. Add the melted butter and blitz until the mixture resembles wet sand. Tip the mixture into the pan. Using a rubber spatula, press crumbs around the side of the pan and press crumbs onto the base of the pan – I use a flat-bottom glass for this. Bake for 10 minutes to set the crust. Let the crust cool. Keep the oven on.

While the crust cools, whisk together the condensed milk, yolks, egg, zest and juice in a medium bowl until well combined. Pour the filling into the cooled crust. Bake for 15 to 20 minutes until almost set, the pie may still be a tiny bit loose in the center but will become more set as it cools. Chill at room temperature for 1 to 2 hours. Cover and chill the pie for 4 hours or overnight. Top with whipped cream to serve. Serves 8.