Peel and cut the quince into quarters, remove the core. Pour enough fresh cold water into a saucepan to cover the quince by 2 cm. Add sugar, chili, ginger, star anise and vanilla pod. Bring to a boil and cook over moderate heat until the quince is soft. Remove the quince from the broth, dry and cut each quarter into two slices.
Preheat oven to 170°C. Grease the bottom and walls of a faience mold with a diameter of 24-26 cm with butter.
In the bowl of a food processor, place the sugar, flour and 200 g of butter cut into pieces. Grind until coarse crumbs form. Add oatmeal and run the processor for another 5 seconds. Spread half of this mixture over the bottom of the mold. Lay out the quince slices, sprinkle with the remaining dough. Spread the remaining butter pieces on top.
Bake the crumble for 40-50 minutes, until golden brown. Cool to room temperature.
Boil the remaining syrup over moderate heat until the consistency of liquid honey, pour into a gravy boat.
Serve the crumble with a scoop of ice cream and sauce.