Crush the biscuits finely by hand or pulse them in a food processor.
Add the melted butter and pulse or stir briefly, just until the crumbs are evenly coated.
Press the mixture firmly over the base and slightly up the sides of a prepared tart dish. Use the back of a tablespoon to create an even crust, then freeze for 10–15 minutes.
Make the Filling
Stir the condensed milk and well-drained crushed pineapple together until evenly combined.
Add the lemon juice and mix until the filling begins to thicken.
Gently fold in the whipped cream, taking care to keep the mixture light and airy.
Spoon the filling over the chilled crust and smooth the top. Decorate with a few biscuit crumbs or small pineapple pieces, if desired.
Refrigerate for at least 3 hours, preferably overnight, until completely set. Slice and serve chilled.
Notes
The yield is estimated at 8 servings and may vary according to the size of the tart dish. Drain the pineapple thoroughly to prevent a loose filling. Keep refrigerated until serving.