In a small saucepan off the heat, combine the sugar and cornstarch. Whisk in the eggs and egg yolk, then add the lemon juice and water. Bring to a boil over medium heat, stirring constantly and scraping the bottom and sides of the pan, until the curd has thickened. Remove from the heat and strain through a sieve. Cover with plastic wrap directly on the surface of the curd and refrigerate for 1 hour or until completely chilled.

Line the bottom of a 6-inch (15 cm) springform pan with parchment paper. Cut another sheet of parchment paper into an 8 x 5-inch (20 x 12.5 cm) rectangle and line the inner walls of the pan. Place in the freezer while preparing the curd.

Using a 2-tbsp (30 ml) ice cream scoop, shape 4 scoops of vanilla ice cream, 3 of raspberry sorbet and 3 of mango sorbet. Place on a parchment-lined plate in the freezer while preparing the trifle. 

Arrange one-third of the cake cubes over the bottom of the pan. Still using the ice cream scoop, arrange a layer of ice cream and sorbet over the cake cubes, alternating the flavours. Drizzle with one-third of the lemon curd. Repeat the sequence twice, using the reserved scoops of ice cream and sorbet to top the trifle. Garnish with the remaining curd. Freeze for 4 hours or until firm. 

When ready to serve, unmould the trifle, cut into wedges and top with the raspberries and raspberry coulis.