Begin by cutting your chilled puff pastry sheets into 5-inch squares. Place them on a lined baking sheet and keep them cold.

In a medium saucepan, melt 2 tablespoons of butter over medium heat. Gradually whisk in 2 tablespoons of flour to form a roux, cooking for about 2 minutes until bubbly. Slowly add in 1 cup of warm milk, whisking until thick and smooth, about 10 minutes.

Remove the béchamel from heat and stir in 1 cup of chopped spinach, 1 cup of diced ham, and half of the cheese. Mix well until everything is coated.

Take a pastry square and place a generous spoonful of filling in the center. Sprinkle with remaining cheese. Fold the corners to seal and form a pocket.

Preheat the oven to 400°F (200°C). Brush each filled pastry with beaten egg. Bake for 20 minutes or until they are golden brown.

Let the puffs cool for a few minutes before serving warm, ideally alongside a fresh salad.