1. Preheat the oven to 200°C (392°F).
2. Slice the onion.
3. Sauté in a pan with butter (add a little water to just blanch, not brown).
4. Cut the zucchini into small squares.
5. Roll out the puff pastry on parchment paper and prick it with a fork (to prevent it from puffing up).
6. Lay the ham at the bottom (leaving the edges free).
7. Make a mixture: 2 eggs, salt, a little heavy cream, grated cheese.
8. Mix in the onion and zucchini mixture.
9. Place everything on one side of the puff pastry.
10. Cover everything with the other side, fold the edges well (to prevent overflow).
11. Make small holes on top (gently).
12. Create a design with a knife (if desired).
13. Brush with egg yolk and a drop of milk and bake for about 15 minutes (depending on the oven).