Roll out the pastry on a floured surface until a little larger than a buttered loose-bottomed fluted tart tin with sloping sides, 20 cm (8 inches) in diameter at the top and 5 cm (2 inches) deep. Press the pastry over the base and sides and trim off the excess so it stands a little above the top of the tin. Prick the base with a fork, then chill for 15 minutes. Bake blind (see
Make the filling. Add the water to a small heatproof bowl, then sprinkle over the gelatine, making sure it is completely absorbed by the water. Leave for 5 minutes. Stand the bowl in a pan of gently simmering water and leave until the gelatine has completely dissolved to a clear liquid.
Purée the strawberries, then sieve. Whip the cream to form soft swirls, then fold in the yogurt, strawberry purée, sugar and vanilla. Gradually add the dissolved gelatine, pour into the tart case and chill for 1 hour.
Make the jelly topping. Sprinkle the gelatine over 2 tablespoons water and leave to soak as before. Add the strawberries to a saucepan with the remaining water and sugar, and cook for 5 minutes, mashing until soft. Take off the heat and stir in the gelatine until dissolved. Purée until smooth, then add the vanilla. Leave to cool.
Pour the jelly over the top of the tart, add the small strawberries around the edge of the tart and chill for 2–3 hours or until set. Remove the tart from the tin, transfer to a serving plate and cut into portions.