Preheat your oven to 400°F (200°C) and grease a 12-cup muffin tin.

In a large skillet over medium heat, melt 2 tablespoons of butter. Add chopped onion and minced garlic, cooking until translucent and fragrant (3-4 minutes).

Add diced chicken and frozen vegetables to the skillet and sauté for 5-7 minutes until chicken is cooked through.

Pour in chicken broth and heavy cream. Season with salt, pepper, and dried thyme, allowing mixture to simmer for 5 minutes until thickened.

Roll out puff pastry and cut into 3-inch squares, pressing them into the muffin tin cups.

Spoon the filling into each pastry cup and cover with additional pastry, sealing edges. Brush tops with egg wash and bake for 25-30 minutes until golden.