Preheat your oven to 400°F and line a large baking sheet with parchment paper. Set it aside.

Cut puff pastry sheets into 5-inch (13cm) squares and refrigerate them.

In a saucepan over medium heat, melt butter, add flour and salt, and cook for 1 minute, stirring frequently.

Slowly whisk in the milk until smooth and boiling. Reduce heat to low, simmer, stirring occasionally until the mixture thickens.

Add spinach, cook for 1 minute until wilted, then stir in ham and 1 cup of Swiss cheese. Remove from heat and set aside.

Arrange puff pastry squares on the prepared baking sheet.

Top each square with a spoonful of ham and cheese mixture, and sprinkle with grated cheese.

Fold the corners up, forming a smaller square.

Brush the pastry with egg wash, ensuring all sides are coated.

Bake for 18-20 minutes or until puffed and golden.