1. Cook the chicken: Heat a pan with a little oil, cook chicken until just golden. Remove and set aside.
2. Sauté the veggies: In the same pan, add butter/oil, onion, leek, carrot, and garlic. Cook until softened.
3. Make the sauce: Sprinkle in flour, stir 1 min. Slowly whisk in chicken stock, then almond milk, stirring until thickened into a creamy sauce.
4. Season: Stir in Dijon mustard (if using), thyme, and a touch of salt/pepper.
5. Add chicken & corn: Return chicken to pan with corn. Simmer 5–7 mins until chicken is cooked through. Mixture should be thick and creamy (not watery).
6. Assemble: Spoon filling into a small pie dish (or 2–3 ramekins for minis). Lay puff pastry over top, trim edges, crimp to seal. Cut a small steam hole in the center.
7. Bake: Brush with egg (optional). Bake at 200°C (fan 180°C) for 20–25 mins until pastry is golden and puffed.
8. Cool slightly before serving (for toddler safety).