Preheat the oven to 190 degrees C and line a baking tray with foil.
Wash and gently scrub the quinces and lay them on the prepared baking tray. Roast for about 1-2 hours in the oven until they feel soft. The cooking time will change depending on the size and firmness of the quinces so keep checking.
Once the quinces have cooled enough for you to touch them cut them open, remove the cores and seeds and the black points with a sharp knife.
Place the quinces back onto the baking tray with the cut side facing up. Add a piece of butter to each quince and sprinkle with 1 tablespoon of sugar.
Roast the quinces again for 30-60 minutes in the oven at 190 degrees C until they are very soft and have taken on a red colour.
At the end you can turn on the grill so that the sugar begins to crystallise. Serve with cream or mascarpone.