Make the crème pâtissière. Bring the milk and seeds from a vanilla pod to the boil.
in a bowl, combine the egg yolks, sugar, cornflour and salt using a whisk.
Temper the egg yolk mixture with the just-boiled milk and return to the sauce pan. Bring to the boil over low heat, whisking constantly.
Pour the crème pat into a heatproof container and cover with clingfilm to the touch.
Refrigerate until cold.
When the crème pat is cold, get on with the crème d’amandes.
Cream the butter, icing sugar and vanilla sugar in the bowl of a stand-mixer fitted with the paddle attachement until light and fluffy.
Add the eggs one at a time, mixing well after each addition.
Add the ground almonds, cornflour and salt and mix to combine.
Then add the crème pâtissière, in three times, mixing well and scraping the sides of the bowl as you do so.
The frangipane is ready to be used.
To make a galette des rois, you will need around 600 g puff pastry. Roll into into two large discs, around 4-5mm thick. Pipe the frangipane in the center leaving a 2cm edge. If you wish, place a ceramic fève in the frangipane - the one who gets it in its slice will be crowned king/queen. Brush the edge with water and top with the second disc of puff pastry, pressing the edges together well.
For a perfect finish, cut around the galette - through both layers of puff pastry to create a neat edge. Use a large plate with the right diameter and a small sharp knife.
If you want, you can then freeze the galette as is for 1 hour, you just want the puff pastry to harden so that it creates a nice flat surface for scoring later.
Then pre-heat the oven to 190°C /fan 180°C. And prepare a baking tray lined with a silicon mat or baking paper.
Place the galette upside-down onto the prepared tray. Brush with a beaten egg yolk and allow to dry 10-15 minutes. Score using the tip of a small knife.
Poke a few holes as well to let the steam escape.
Bake for 40-45 minutes until golden brown.
In the meantime, make the glazing syrup: bring the water and sugar to the boil, with perhaps a pinch of salt. When the galette is ready, brush immediately with the syrup.
Leave to cool slightly and serve in wedges.