Place one sheet of puff pastry on a greased baking sheet.
Prepare the almond mixture: soften the butter and add the sugar. Beat vigorously to obtain a smooth texture.
Add the ground almonds, then the two eggs and the vanilla extract.
Place the almond mixture in the centre of the round-shaped pastry and spread it evenly up to 2cm away from the edge.
Add the lucky charm near the edge (if you add it near the centre, it might be easily discovered when cutting the cake!)
Cover the base with the second round-shaped pastry and ensure the two pastry sheets are stuck together. Otherwise, the almond mix may slip away from the cake when cooking. You may use water to join the two sheets along the edges.
Make an egg wash with the egg yolk and a little water, and using a pastry brush, brush all over the top.
Trace decorative shapes (diamonds, flowers or any other creative designs) carefully with a knife. Make sure you don’t press too hard to avoid piercing the pastry.
Preheat the oven to 200 degrees C and cook at 180 degrees for about 40 minutes. Check on it regularly as our oven cooked it much quicker (25 mins).
Mix the icing sugar with water to make a liquid sugar syrup and spread it over the galette's top.
Cook the galette for 5 minutes at 200 degrees C to allow the sugar to cook slightly and create a shiny effect. Take it out of the oven.
Eat the cake lukewarmly and enjoy the party!