Butter one side of parchment paper and place (buttered side up) into an 8 x 8 ceramic dish. Set aside for later.
Wash and remove the fuzz off the quince, especially if freshly picked. The fuzz will most likely already be cleaned off from store-bought quince.
Chop the quince into chunks. You can either peel them, or leave them as is. You will have a smoother texture in the end if you peel them. I didn’t peel mine, but I will the next time!
Place chopped quince in a 6 quart saucepan and cover with plenty of water.
Bring to a boil and cook, covered, for 40 minutes, or until the fruit is fork-tender.
Once done, drain into a strainer.
Puree the quince in a food processor until you achieve an apple sauce consistency. Using a kitchen scale, weigh the quince puree, then add back into the empty saucepan.
Weigh out an equal amount of sugar and add to the quince. In my case it was a pound of each. Stir over low-medium heat until the sugar liquifies. Slit the vanilla bean down the center and add to the same pot.
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.
This is what the quince looked like after 1 1/2 hours of cooking time.
Using a spatula, transfer the mixture into the prepared dish.
To achieve a smoother surface, I used a buttered sheet of parchment paper to cover the membrillo. I then ran my hands over the parchment paper to smooth out the surface.
Refrigerate the membrillo for a couple of hours until it sets. To serve, cut into squares and serve with Manchego cheese and a nice glass of wine.