1. Cut the fish into small pieces and half of the prawns in 2.
2. In a mixer bowl, mix the fish and half of the prawns with the cream, egg whites, Cayenne pepper, salt, and pepper. Incorporate the chopped herbs. Mix until you get a smooth paste. Reserve 30 minutes in the refrigerator.
3. Line a buttered tart pan with a sheet of pastry. Pinch the edge at regular intervals. Put in the refrigerator.
4. Preheat the oven to 180°C.
5. Dip the broccoli in boiling salted water for 2 minutes. Drain.
6. Spread half of the fish filling over the bottom of the tart; cover with broccoli and the remaining prawns. Cover with filling and press well.
7. Cover the filling with a second sheet of pastry and seal by gluing the 2 sheets with a little cold water. Prick the tart with a knife. Brush with beaten egg.
8. Bake for 40 minutes. Remove from the oven and serve immediately.