Lightly grease a 10cm x 35cm rectangular loose-bottom tart tin. Place biscuits into a food processor and blend until the mixture resembles fine crumbs. Pour in 125g melted butter and pulse to combine. Press mixture into prepared pan and chill.
Combine the icing sugar with the corn flour.
Process 2 tablespoons of this icing sugar and mix with half the strawberries until smooth. Pass through a sieve to remove seeds.
Melt the white chocolate in a bowl set over a pan of gently simmering water.
With a mixer or processor, beat cream cheese and remaining icing sugar and cornflour until smooth.
Add melted white chocolate, 2 tablespoons of strawberry purée and dried strawberry powder. Mix well. Spread mixture into prepared pan and chill for
2-3 hours until cold, or leave overnight in the fridge.
When the filling is cool, melt the dark chocolate and the extra l tablespoon of butter together in a bowl set over a pan of simmering water. Stir until smooth and spread over the top of the tart. Chill for 20 minutes or until set. Decorate with remaining strawberries and edible balls, if using. Serve in slices with remaining strawberry purée on the side.