Preheat your oven to 400°F (200°C) and gather your ingredients and muffin tin.

Melt 2 tablespoons of butter in a large skillet over medium heat. Add chopped onion and minced garlic, cooking for 3-4 minutes until translucent and fragrant.

Introduce diced chicken breasts and frozen mixed vegetables to the skillet, stirring for 5-7 minutes until the chicken is cooked through.

Pour in chicken broth and heavy cream, season with salt, pepper, and dried thyme. Simmer for about 5 minutes until thickened.

Roll out puff pastry on a floured surface, cut into squares and press into muffin tin holes to form cups.

Fill pastry cups with the creamy chicken filling about three-quarters full, cover with smaller squares, seal edges and brush with egg wash. Bake for 25-30 minutes until golden.