Peel, core, and slice quince into 1-2cm thick pieces.
Place a 6-inch cast iron pan on medium heat. Add caster sugar bit by bit to make a dry caramel. Avoid going too dark at this stage - you want pale golden.
You can add the butter when there’s still a few grains of sugar undissolved. Add butter along with the sprigs of rosemary and a pinch of flaky salt. You can also add chopped walnuts here, if desired.
Arrange quince slices in the pan, thick side down. Cook quince on medium heat for 10-15 minutes with a lid (or a piece of parchment paper to help them steam) until slightly softened - you should be able to pierce with a knife easily.
While quince cooks, preheat the oven to 180c fan.
Roll out the pastry thinly, about 0.25cm. Once quince is tender, drape the pastry over it. Tuck edges inside the pan. Cut a small slit on the pastry.
Place pan in preheated oven, and bake for 18 minutes, or until golden.
Allow the tart to cool for 5 minutes, then invert onto a serving plate. Serve warm, optionally with ice cream or whipped cream.
