This recipe is courtesy of Simply Recipes.
Put quince pieces in a large saucepan and cover with water. Add vanilla pod and lemon zest, and bring to a boil. Reduce to a simmer, cover, and let cook for 30-40 minutes, until you can easily pierce the quince pieces with a fork.
Strain the water from the quince pieces. Discard the vanilla pod, but keep the lemon peel with the quince.
Purée the quince and lemon peel in a food processor.
Measure the purée: You will need to use the same amount of sugar as purée, i.e. if there are 4 cups of purée, use 4 cups of sugar. Return the quince purée to the saucepan, and begin to heat gently. Add the measured quantity of sugar.
Heat on medium-low, stirring until the sugar has completely dissolved. Add the lemon juice.
Continue to cook on a low heat, stirring occasionally, for 1 – 1 ½ hours, until the paste is thick and has a deep orange-pink color.
Preheat the oven to 125 degrees F. Line an 8”x8” baking pan with parchment paper. Lightly grease the parchment paper with butter.
Pour the quince paste into the baking pan. Smooth out the paste so that it is evenly spread.
Place in the oven for an hour. Remove from oven and let cool.
When cool, serve by cutting into squares or wedges. Store in the refrigerator, wrapped in foil or plastic wrap.