Place the quince pieces into a large pan and add enough water to cover. Add the vanilla pod and bring to the boil. Place a lid on the pan and boil for 30-40 minutes, or until quinces are very soft.
Drain the liquid from the quinces and transfer the quinces to a scale to weigh. Note the weight of the quinces - this is the weight of caster sugar you will require.
Place the fruit into a food processor and blend until very smooth.
Return to the original pan and add an equal weight of sugar.
Cook over a low heat, stirring constantly, until the sugar dissolves.
Continue to cook over a low heat, stirring occasionally, for 1-1½ hours, or until the quince paste has thickened and has a deep orange colour.
Preheat the oven to 50C/120F.
Pour the cooked paste out onto a greased and lined 20cm/8in x 20cm/8in baking tray and smooth the paste out evenly.
Place into the oven for one hour to speed up the setting process.
Remove from the oven and slice into manageable portions.