Blend mango flesh to a smooth puree and strain if fibrous.
Whisk mascarpone and sugar until smooth.
Add mango pulp and whisk just until combined.
Add chilled heavy cream and whisk to soft peaks; do not over-whisk.
Prepare the soak
Mix mango pulp with water and optional cardamom in a shallow bowl.
Assemble layers
Dip each biscuit quickly in the soak and arrange one layer in the dish.
Spread half the mango cream, then sprinkle fresh mango cubes.
Repeat with a second biscuit layer and remaining cream.
Smooth the top or pipe cream swirls for a decorative finish.
Chill and serve
Refrigerate at least 6 hours or overnight.
Top with mango cubes and silvered pistachios just before serving.
Notes
Over-soaking biscuits causes a soggy base. Dip briefly and let excess drip.If using canned mango pulp, reduce sugar because many brands are pre-sweetened.For clean slices, chill overnight before cutting.Store covered in the refrigerator for up to 3 days. Do not freeze.