1) Make the crust: Place digestive biscuits in the bowl of a food processor and pulse until crumbs are formed. Add butter, brown sugar and salt and pulse to incorporate, until crumbs resemble wet sand. Coat an 20cm square pan with cooking spray and pack crumbs firmly into the bottom of it. Refrigerate until ready to use.
2) Make the filling: In a large bowl, combine cream cheese, condensed milk and pasteurized egg product and beat on high with an electric mixer until smooth and creamy, about two minutes. Add lemon zest and juice and beat until fully incorporated, another 30 seconds. In a small bowl, combine the gelatin and boiling water and whisk until gelatin is entirely dissolved; let cool two to three minutes. Stir the gelatin into the cream cheese-lemon mixture until well incorporated. Pour the filling over the crust. Refrigerate for eight hours or overnight, until filling is firm. Slice into 5cm squares using a chilled knife coated with cooking spray.