To make the syrup, add the prepared quince, water, sugar, lemon peel, and cardamom pods to a saucepan.
Bring to a boil and then simmer gently until the quince are fork-tender. This can take anywhere from 15 minutes to 45 minutes, depending on how ripe your quince are, so check regularly.
Strain the syrup through a muslin, allowing the quince half an hour or so to fully strain through.
Refrigerate the quince-cardamom syrup until ready to use.
To make the white wine spritzer, first add the ice to a large wine glass.
Add 1 ounce of quince cardamom syrup and the Lillet Blanc to the glass.