To make the basil pesto whizz the pine nuts, basil, garlic and parmesan in a food processor to a rough paste. With the motor running slowly trickle in the olive oil. Season to taste.
For the tartlet casings bake the Vol au Vents as per the manufacturers recommendations.
Skin the plum tomatoes by cutting a cross in the top of the tomato and place them in boiling water for 5 to 10 seconds. Take them out of the water and place them in a ice water bath immediately. Take the tomatoes out after 1 minute and take the skins off.
Cut the tomato in half and remove the seeds and pulp. Using one half of the tomato cut a 4cm round shape out of the tomato using a pastry cutter. Do this for all on the tomatoes. Leave all of the tomato rounds on a tray seasoned and drizzled with olive oil and some basil leaves to marinate.
With the leftover tomato trimmings cut into strips and then into small cubes. When all the cubes have been chopped place into a bowl with some basil and olive oil. Season also. This is called tomato concassé.
Slice the mozzarella into manageable slices.
To arrange take a Vol au Vent casing and place mozzarella in the bottom. Spoon over some of the tomato concassé and drizzle with basil pesto. Arrange five of the round tomato slices nice and neatly over the top. Repeat this process until, you have all the cases filled.
Bake for 10-15 minutes at 180°C or until the mozzarella has melted. Serve with a drizzle of basil pesto on top of the tartlet