Crush the biscuits in a food processor and pour in the melted butter. Blitz once to mix well.
Press this to form an even layer on the bottom and along the sides of a 20 cm springform pan. Chill for 45 minutes in the fridge for the the base to set.
Melt the chocolates in a double boiler over barely simmering water. Mix with a spatula to combine both chocolates. Set aside to cool slightly.
In another bowl, whisk together the cream cheese and the mascarpone till you get a smooth and silky texture.
Stir in the melted chocolate and mix well. Pour the cheesecake mixture onto the set biscuit base and chill for 4 hours till it has set completely. Decorate with sliced strawberries.