Line the base and sides of a 20cm round springform tin with baking paper.
Remove the ice-cream from the freezer and allow it to soften but not melt.
Crush biscuits until they resemble fine bread crumbs and place in a large bowl.
Heat butter in a microwave safe bowl until just melted. Add melted butter to the crushed biscuits and stir to combine.
Put the biscuit mixture into the bottom of the springform pan and push down with the back of a spoon to flatten.
Place softened ice-cream in a large mixing bowl and gently stir through ½ punnet of each type of berries.
Spoon the ice-cream on top of the biscuit base evenly. Smooth to flatten the top with the back of a spoon. Cover the top with baking paper or gladwrap and place in the freezer to set overnight.
To decorate, place caster sugar in a bowl; whip eggs whites on high until stiff peaks form. Using a small paintbrush, brush each piece of remaining fruit with the egg white and then sprinkle with sugar.
Place on a tray lined with baking paper to dry. They will harden in a couple of hours.
When ready to serve, remove the ice-cream cake from the freezer, unmould from the springform tin, place on a serving plate and top with the sugared berries.