Start by preheating your oven to 400°F (200°C). Place the thawed puff pastry sheet on a floured surface. Roll it out slightly to ensure it’s an even thickness. This will make cutting out your bites easier.

Using a sharp knife or a pizza cutter, slice the pastry into squares, around 2-3 inches in size. You want them bite-sized but not so small that they lose all that delicious filling.

In a small skillet, melt the butter over medium heat. Whisk in the flour, cooking for about a minute until it forms a roux. Gradually add the milk while whisking continuously to avoid lumps. Continue cooking until the mixture thickens, about 3-5 minutes. Stir in the salt, thyme, Dijon mustard, and nutmeg. Set aside to cool slightly.

In a bowl, combine the diced ham, Gruyère, Emmental, Parmesan, roasted garlic powder, crushed dried thyme, and black pepper. This cheesy mixture will be heavenly, making your bites rich and satisfying.

Lay out half of your pastry squares on a baking sheet lined with parchment paper. Spread a thin layer of Dijon mustard on each square. Then, spoon in the ham and cheese mixture generously. Top with a drizzle of the béchamel sauce. Place another pastry square on top of each filled square, pressing down lightly to seal the edges.

Using a small bowl, beat the egg with a fork. Brush the tops of each pastry square with the egg wash. This will help them achieve that golden color and flaky texture in the oven.

Place the baking sheet in the preheated oven and bake for 15-20 minutes, or until the bites are golden brown and puffed up. The aroma will fill your kitchen, making it very hard to resist until they’re cool enough to handle!