Sift the flour and salt in a large bowl. Whisk together egg in a small bowl. Add the sugar to the flour mixture and mix well.
Add the butter in the flour mixture and work with hands gently until it resembles fine breadcrumbs. Finally add the egg and knead the dough together
Flatten the dough, wrap it in a cling film and refrigerate for minimum of two hours or overnight.
Prepare the pastry cream:
Whisk together the egg and sugar until it resembles very pale and creamy. Add the flour to the egg mixture and whisk well until it gets incorporated.
Heat the milk and extract in a pan until it reaches just under boiling point. Pour the milk little by little into the egg mixture and whisk well. Return the mixture to the heat again and keep stirring well until it becomes thick custard.
Pour the custard in a bowl and cover the top with cling film to avoid forming film on top. Allow the filling to cool completely, you can make it the previous day and store it in the refrigerator.
Assemble the tart:
Preheat the oven to 180 degree Celsius.
Take the dough out from the refrigerator, roll it out between two cling film or parchment paper. Gently place the rolled dough in a greased tart tin. Press the edges down. Prick with a fork all over the dough. Trim all the dough in the sides. Place a parchment paper on top of the dough and fill with baking beans. Blind bake for 5 mins
Allow it to cool completely. Pour the custard inside the tart case. Sprinkle the grated nutmeg on top. Bake for 35 to 40 mins or until golden brown on sides.
Let it cool down for a while and serve it into wedges.