Bring a pot of water to a boil. Trim the green tops and roots. Score and peel the leaves carefully to avoid tearing.
Wash and blanch the leaves in boiling water for about a minute, then set aside to cool.
Combine all filling ingredients in a bowl.
Lay a leek leaf flat, place a spoonful of filling at one end, fold into a triangle, and continue folding along the leaf.
Arrange the stuffed triangles in a baking dish.
Whisk together all sauce ingredients.
Preheat oven to 200°C on turbo mode.
Pour the sauce over the leeks, cover with damp parchment and foil, and bake for 75 minutes.
Increase oven temperature to 220°C, remove the cover, add more water if needed, and bake for an additional 15 minutes until golden.
