Mix all the ingredients. If you're using frozen berries then let them thaw on a sieve or colander over a bowl so they can let go of their excess liquid.
Place the filling onto the base and help it flatten out using a spoon or spatula.
Bake the tarts in a preheated oven at 180C / 350F for 30-40min. It's important that you notice that the filling is bubbling. This is the process that cooks out the cornstarch and helps the filling thicken.
Let the tarts cool down once removed from the oven. When they're cold enough to manipulate then you can unmould them.
Serve the warm tarts with vanilla bean ice cream and leaves of basil or mint.