Butter one side of parchment paper and place (buttered side up) into an 8" x 8" or 5" x 7" ceramic pan. Set aside for later.
Wash and remove the fuzz off the quince, especially if freshly picked.
Chop the quince into chunks.
Place chopped quince in a six-quart pot and cover with four cups of water.
Bring to a boil and cook, covered, for 30 minutes, or until the fruit is fork-tender.
Once the quince is tender, drain into a strainer.
Puree the quince in a food processor until you achieve an applesauce consistency.
Using a kitchen scale, weigh the quince puree, then add back into the empty pot.
Weigh out an equal amount of sugar and add to the quince.
Stir over low-medium heat until the sugar liquifies.
Slit the vanilla bean down the center and add to the same pot, or use vanilla extract.
Stir frequently while cooking. You will notice that the color of the quince will begin to deepen the longer it cooks.
After about an hour of cooking, remove the vanilla bean and stir in the lemon juice.
Continue to cook, stirring frequently, for an additional hour.
Using a spatula, transfer the mixture into the prepared pan.
Refrigerate the membrillo for a couple of hours until it sets.
To serve, cut into squares and serve with Manchego cheese, crackers, and wine if desired.