Preheat the oven to 325 F (160 C).
Wash the quinces well, then set them aside.
In a saucepan, bring the water and sugar to a boil, stirring to dissolve the sugar.
Let boil for one minute, then add the vanilla powder.
Peel the quinces, keeping the skin, and cut them in half lengthwise.
Remove the core, then place the quince halves in a baking dish, rounded side down, and add the skin.

Drizzle with syrup and cover with aluminum paper.
Bake for 2 hours 30 minutes, taking care to turn them every 30 minutes.

Transfer the cooked quinces to a dish with a slotted spoon.
Strain the cooking liquid through a fine mesh into a saucepan.
Add the lemon juice and bring to a boil, then let boil for 15 minutes or until the liquid is reduced by half.
Set the syrup aside.