To make the strawberry puree:
Tip the frozen strawberries into a large bowl and leave to thaw. This can take a few hours. Once thawed, add the strawberries and their juice to a food processor or blender and blitz until puréed .Pour the puree into a bowl. Add the sugar and stir until the sugar dissolves. Add a little lemon juice to taste. Sieve the strawberries if you don’t want any seeds.
To make the crust:
Preheat oven to 160°/ 350°F. Grease a 10-inch-diameter springform pan with 3-inch-high sides and surround the pan with tinfoil. Mix together digestive biscuits, melted butter and sugar in processor. Blitz until mixture resembles crumbs. Press crumbs onto bottom and 2 3/4 inches up sides of springform pan. Bake in the oven for 10 minutes. Transfer to rack and cool while making the filling.
To make the filling:
In a freestanding bowl with electric mixer, beat cream cheese in large bowl until light. Add in sugar and mix well. Beat in eggs gradually and then add in sour cream, whipping cream and vanilla and beat.
Transfer about one third of the filling to the crust. Spoon 4-5 small spoonfuls of strawberry puree on top and swirl it through the filling using a knife. Repeat by layering the filling and purée. Finally, with the knife, swirls purée through filling to create the marbled effect on the top of the cheesecake. Be as decorative as you wish!
Place the pan into a large roasting pan. Pour boiling water into roasting pan to cover halfway up the sides of the springform pan. Bake until cheesecake begins to puff around the edges,. This usually takes about an hour and 15 minutes. Remove cake and leave to stand in the tin for about an hour before placing on a wire rack, loosen the edges with a knife and leave to cool fully. Remove from the tin and chill for at least 4 hours in the fridge, although overnight is preferable. Drizzle remaining strawberry purée over the cake before serving.