I developed this recipe for an Istrian themed Secret Kitchen dinner as a nod to Croatia's Habsburg past. I am grateful to Felicity Cloake for her strudel research and tips, some of which is incorporated here.
In association with Riverford, the lovely organic veg box people, I offer seasonal preserving workshops. I cover all the basics of preserving fruits and vegetables and together we make five you can take home. 
Location: London N5
The trick is to avoid graininess, a common flaw. Quinces have tiny rock-hard grains in their cores, which will pass through just about any sieve. Most recipes tell you to cook whole quinces then blitz and sieve the lot, but this results in grainy membrillo. So remove the cores before or after boiling the quinces. I prefer after, as a) cutting cores out of raw, hard quinces is tricky, and one of these days I will slice right into my hand, and b) the cores and pips help add colour and pectin, so better to leave them in until just before you sieve.
My wooden crate of beautiful yellow, fuzzy fruit, looking a bit like misshapen fat pears, is rapidly emptying as I work my way through the quince wish list I’ve been compiling for several years...
Balıkçı Sabahattin, a fish restaurant frequented by wealthy locals, proved perfect. The fish börek, marinated bass and scorpion fish soup were delicious, but the highlight came after - ayva tatlısı - half a quince, candied to a translucent deep crimson, topped with the thickest, lushest cream imaginable and ground walnuts, and surrounded by a moat of spicy syrup. It was divine, and thankfully cropped up again several times on our journey through Turkey. The cream turned out to be kaymak - clotted cream made from buffalo milk.
Many people poach the quince in a syrup on the hob. But this slow-roasted method comes from Őzge Samancı, a food historian in İstanbul we were lucky enough to meet. If you roast them for an hour they will be perfectly tender and delicious, but still yellow. If you continue another couple, they will turn a beautiful pink. And I’ve found that if you continue another three or so after that, they will almost candy themselves and reach the desired depth of colour. If you can’t get buffalo clotted cream, cow’s will of course do, as will any thick cream or yoghurt.
This is a standard jelly recipe, so you could use cooking or crab apples instead, or half apples and half hedgerow berries - rowans, rosehips, sloes, blackberries, elderberries and haws all work well. It helps to squish the simmering fruit with a potato masher once or twice, to ensure all the flavour comes out. You can also flavour such jellies with a little spice or herb, by adding these to the simmering fruit at the first stage.
