Peel, halve, and core the quinces.
Place quinces in a saucepan with sugar and water, then bring to a simmer.
Poach the quinces for 3 hours on very low heat until tender and a vivid red colour develops from the anthocyanins.
Turn off the heat and allow the quinces to cool completely in their poaching liquid.
Meanwhile, roll out flaky pie dough into a rough round shape and place on a lined baking sheet.
Boil down some of the quince poaching syrup until it becomes thick and scoopable to make quince jelly.
Slice the cooled quinces and arrange them on top of the pie dough, folding the edges up over the fruit.
Brush the quinces with quince jelly for extra flavour and shine.
Bake the galette in a preheated oven until the pastry is golden and crisp.
Serve warm with a side of cold whipped cream.