Preheat the oven to 220°C.
Remove the two layers of puff pastry from the package and spread them out on a lightly floured work surface. Cut out a circle about 24 centimeters in diameter from each layer. Place one of the circles on a baking tray lined with parchment paper.
To make the frangipane, mix the cooled crème pâtissière with the crème d'amande until smooth, and pour onto the dough circle on the baking tray. Spread with a spoon or spatula so that the mixture forms a slight dome toward the center, leaving a two-centimeter border all around. Hide the figurine in the frangipane.
Whisk the egg yolk with the cream and brush the edge with it. Place the second dough circle over the filling and gently press down on the edges. Score decorative patterns with a sharp knife (I made a crown) and poke small air holes in a few places to prevent the galette from collapsing after baking.
Brush the galette with the remaining egg mixture, leaving the edges free so that the puff pastry can rise nicely.
Bake in the preheated oven on the middle rack for 15 minutes, then lower the temperature to 180°C and bake for another 15 minutes.
Optional: Dust the galette des rois evenly with a little powdered sugar and bake for another ten minutes, until the sugar has melted into a shiny caramel. Let cool slightly and serve immediately.