Make the base: Butter and line a 23cm loose-bottomed tin with baking parchment. Put 250g digestive biscuits in a plastic food bag and crush to crumbs using a rolling pin. Transfer the crumbs to a bowl, then pour over 100g melted butter. Mix thoroughly until the crumbs are completely coated. Tip them into the prepared tin and press firmly down into the base to create an even layer. Chill in the fridge for 1 hr to set firmly.
Remove the vanilla seeds from 1 pod: Slice the vanilla pod in half lengthways, leaving the tip intact, so that the two halves are still joined. Holding onto the tip of the pod, scrape out the seeds using the back of a kitchen knife.
Make the filling: Place 600g soft cheese, 100g icing sugar and the vanilla seeds in a bowl, then beat with an electric mixer until smooth. Tip in 284ml pot double cream and continue beating until the mixture is completely combined. Now spoon the cream mixture onto the biscuit base, working from the edges inwards and making sure that there are no air bubbles. Smooth the top of the cheesecake down with the back of a dessert spoon or spatula. Leave to set in the fridge overnight.
Un-moulding and topping: Bring the cheesecake to room temperature, about 30 mins before serving. To un-mould, place the base on top of a can, then gradually pull the sides of the tin down. Slip the cake onto a serving plate, removing the lining paper and base. Purée half the 400g punnet strawberries in a blender or food processor with 25g icing sugar and 1 tsp water, then sieve. Pile the remaining strawberries onto the cake, then pour over purée.