In a large pot, heat oil and add onion, carrot, and green curry paste. Stir and cook for 2-3 minutes.
Add garlic, ginger, kaffir lime leaf, chicken, coconut milk, and chicken stock. Stir well and let simmer for 15 mins, until carrots are tender and chicken is cooked through.
Taste and adjust by adding fish sauce or salt, or sugar for sweetness if needed.
In a small bowl, mix cornstarch with a small amount of water to create a slurry. Add to the simmering sauce to thicken.
Remove pot from heat and transfer curry into a baking dish and let cook for 10 mins.
Once cooled, place pastry sheet over the mixture. Brush with whisked egg wash to ensure a golden finish.
Use a fork to create small holes in the patry, and sprinkle black sesame or poppy seeds to garnish.
Bake in oven for 15-20 mins, or until the puff pastry turns golden.