Whisk cream, sugar, yolks, milk and cornflour till smooth. Stir over medium-low heat till thick enough to coat pot thinly (or metal spoon if using non-stick pot). Place pot in water-bath. Add vanilla extract. Stir till mixture is half-cool. Leave to cool completely.

Preheat oven to 250°C. Line baking tray with aluminium foil, shiny side up.

When oven is ready, remove pastry shells from freezer. Place slightly apart on baking tray. Fill shells with custard to 5 mm from edge. Bake till crust is brown, and custard is burnt and just stops bubbling. This takes 30-35 minutes. Check every 10 minutes and rotate tray as necessary so that all tarts brown evenly.

Remove tarts from oven to wire rack. Leave till cool. Serve within a few hours whilst pastry is crisp.

Leftovers should be unmoulded before pastry softens, then refrigerated uncovered (make sure there isn't any funky odour in your fridge). Reheat tarts on foil lined baking tray at 200°C. Pastry would turn soggy after 5 minutes, then crisp up nicely after another 5 minutes or so. Custard would be creamy and smooth but a bit sunken.