Put the cream, milk and sugar in a large saucepan. Scrape the seeds from the vanilla bean and add to the liquid, along with the vanilla bean. Heat gently over low heat, stirring until the sugar has dissolved. Bring slowly to a boil, and then turn down to a simmer for 5 minutes. Remove the pan from the heat and discard the vanilla pod.
Meanwhile, soak the gelatin leaves in cold water for 5 minutes. Drain and squeeze the gelatin leaves to remove the excess water and add the cream mixture, whisking until dissolved. Pass through a sieve, leave to cool in the fridge for about 10 minutes.
Place 4 plain tartlet molds on a baking sheet. Grease the molds with a drop of oil then line with plastic wrap, leaving the excess hanging over the sides.
Arrange the Sweet Tomato Petals over the bottom of each mold. Pour in the panna cotta and refrigerate until set, about 2 hours.
To serve, gently pull the ends of the plastic wrap to loosen the panna cotta from the sides of the molds. Invert each one on to a plate and carefully shake to loosen. Remove the plastic wrap, and then garnish with dots of aged balsamic and basil leaves.
Sweet Tomato Petals:
Put the sugar and 1 cup water in a medium saucepan. Dissolve the sugar over low heat, stirring from time to time. Once the sugar has dissolved, increase the heat and bring to a boil. Cook for 5 minutes. Remove from the heat and drop in the tomato petals. Steep the tomatoes in the sugar for 20 minutes.
Preheat the oven to 350 degrees F.
Remove the petals from the syrup and drain on paper towels. Line a baking sheet with parchment paper and place the petals on top. Place in the oven for about 5 minutes, turning over halfway, until they dry out a little.