Step 1: Prepare the base. In a medium bowl, combine the finely crushed digestive biscuits with the melted butter. Mix well until the crumbs are evenly coated.
Step 2: Press the biscuit mixture firmly into the base of a 20x20 cm (8x8 inch) square tin lined with baking paper, with an overhang on two sides for easy removal. Place in the refrigerator while you prepare the filling.
Step 3: If using gelatin, sprinkle the gelatin powder over the hot water in a small heatproof bowl. Stir until completely dissolved and set aside to cool slightly.
Step 4: In a large bowl, using an electric mixer, beat the softened cream cheese until smooth and creamy, ensuring no lumps remain.
Step 5: Gradually beat in the sweetened condensed milk until fully incorporated and smooth.
Step 6: Gently fold in the mango puree and passionfruit pulp. If using, fold in the cooled gelatin mixture.
Step 7: Pour the cream cheese mixture over the chilled biscuit base in the prepared tin. Gently tap the tin on the counter a few times to release any air bubbles and smooth the top.
Step 8: Cover the tin with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, until the slice is completely set.
Step 9: Once set, use the baking paper overhang to carefully lift the slice out of the tin. Slice into squares or bars using a sharp knife dipped in hot water for clean cuts.
Step 10: Garnish with extra fresh mango pieces and passionfruit pulp before serving, if desired. Enjoy your tropical treat!