In a small milk pan, gently warm the milk over a medium heat but do not allow it to boil.
Whilst the milk is warming up, in a large jug whisk the egg yolks and caster sugar together with a fork until it become lighter in colour and a creamy consistency.
Once your milk has warmed up, pour it into the jug over the egg/sugar, continuing to stir the mixture whilst you do.
Remove your pastry casings from the fridge and pour the custard evenly into each tart; they should be nearly full. Then sprinkle a little pinch of nutmeg on top of the custard in each tart.
Very carefully (because your custard can spill!), pop the tarts into your pre-heated oven and bake them for 20-25 minutes. Allow the tarts to cool in the tray for at least 15 minutes before transferring to a wire rack to cool completely, or enjoy whilst still warm.