Preheat the oven to 400°F (200°C).

Roll out the puff pastry sheets on a lightly floured surface. Cut out circles (about 4 inches in diameter) and place them on a parchment-lined baking sheet.

Use a smaller round cutter (or a sharp knife) to score a circle about 1 inch from the outer edge of each larger circle, being careful not to cut all the way through.

Brush the beaten egg over the puff pastry circles.

Bake the pastry in the preheated oven for about 12-15 minutes until puffed and golden brown.

In a saucepan, melt the butter over medium heat. Sauté the diced onions and sliced mushrooms until softened.

Sprinkle flour over the mixture to create a roux, then slowly add the heavy cream, stirring until thickened.

Add the shredded chicken, salt, and pepper to the mixture, and mix well.

Carefully remove the tops from the puff pastry shells and fill them with the creamy chicken mixture.

Place the tops back on and garnish with fresh parsley.

Serve warm or at room temperature, paired with a fresh mixed green salad or a side of roasted vegetables.