Eat it. This is food for a special hot day. Take your frozen quince, one very sharp knife, and as soon as the quince is able to be cut into like hard ice cream, cut thin slices and eat it hand to mouth. Do not arrange it on a plate, tart it up, think that it's good for entertaining. If you cut yourself, that's part of the learning experience. I have, when the quince was still too icy, and the visual feast was worth the mess.
What does a frozen quince taste like? More refreshing than any drink or any other solid food. In your mouth, the juices demand to be sucked out, and the astringency that's left in a frozen ripe quince is just the right counterpoint to a hot day, or a hard job done.
Just right, that is, if you like grapefruit, tonic water, lemons, citrus rind, good strong tannic tea. Frozen, you lose the incomparable perfume of a quince, but there is a taste and texture to a frozen quince that is special in its own way.
Eating a frozen quince, slice by slice, isn't a public statement as much as a private pleasure, or an intimate pleasure to share. This is not dinner party food. A frozen quince must be eaten frozen, not when the conversation lags. Once thawed, it needs to be cooked as it rapidly changes from crisp, to rubbery as an old carrot.
I haven't mentioned putting anything on the frozen quince, as it's excellent on its own (if you've got a good quince. This is a ripe Smyrna).
There's only one thing that I think is possibly better than frozen quince slices neat, and that is frozen quince slices dipped in pomegranate paste. At the right time, this is the ultimate comfort food.
Defrosted frozen quinces are lovely, too, when cooked. Here's the recipe for this dish of baked, defrosted quince in its nectar.
Fill your dish with frozen quince and when all defrosted, add water up to about a third the height of the quinces. Bake, covered in a slow oven till they turn whatever shade of red you like (these took two hours).
Do not add anything else to them before baking. To be eaten at any temperature you wish, these are deliciously refreshing, too, without any added sweetener. They are glorious with a dollop of rich yogurt, and go wonderfully with meats and cheeses.
The nectar/ syrup tastes as good as it looks.
If you like fussing, top these quinces with rich yogurt and top that with dribbled pomegranate paste, and top that with chopped walnuts or pistachios.