Roughly slice 500g of the strawberries. Place into a heatproof bowl along with the sugar and vanilla pod and cover with cling film.
Place over a bain-marie and simmer for 30 minutes until all the juice is extracted. Pass the liquid off, add a little lemon juice along with one gelatine leaf for every 100ml of liquid.
Line a suitable mould with cling film and lay the other 250g of strawberries in the bottom before pouring over the jelly. Allow to set in the fridge for 3-4 hours.