Making membrillo is like making bread or soufflé or caramels — when it works, you’re hooked, the dramatic transformation inspiring you to experiment more. When cooked, the flesh of the quince transforms from white to a glorious rose and the once astringent taste becomes sweet and floral. There is nothing tricky about making membrillo — it just takes patience: the quince first simmer for an hour-and-a-half, then cook down with sugar for another hour. Membrillo keeps for months and is such a treat to have on hand this time of year to serve on cheese plates for impromptu gatherings and to give to friends paired with small wedges of various cheeses for holiday gifts. —Alexandra Stafford
Wash quinces and remove any stickers, fuzz or leaves. Cut straight down around the core to remove the flesh, then cut into big chunks and discard the core. Place quince pieces in a large pot and cover with about 6 cups water. Cut lemon in half and juice into pot. Gently simmer until the pieces are very tender, about 1½ hours. Note: if water boils off so that the quince are not submerged, add enough water to cover the quinces and bring back up to a simmer.
Drain the quince pieces. Pass through a food mill. If you don't have a food mill, purée in a food processor. You should have about 3 cups of purée. While you don't have to, it's helpful to measure the amount of purée you end up with as you want to add an equal amount of sugar in the next step.
Transfer purée to a large non-stick sauté pan. Add about 3 cups of sugar (depending on the amount of puree you measured) and cook over low heat, stirring frequently for about an hour. If you get impatient, it's OK to turn the heat up to medium, but keep a close watch on it and stir frequently. The mixture will thicken and will be rosy in color. It will start bubbling almost as a complete mass and will be shiny when done.
Line a sheet pan with parchment paper. (It's helpful to use clips of some sort to secure the parchment to the sheet pan.) Spread the quince paste so that it is about a half-inch thick. Smooth with a spatula and try to form into an even rectangle—it most likely will not cover the whole surface area of the pan. Set aside to cool completely.
When cool, transfer parchment paper-filled membrillo to a large cutting board. Fill a large vase or cup with hot water and have a clean towel by your side. Line a glass storage vessel with parchment paper. Cut membrillo into 2x4-inch pieces approximately, dipping the knife into the hot water and drying it off as necessary. Fill one layer of the storage vessel with cut membrillo, top with another layer of parchment and continue filling in this manner until all of the membrillo is cut.
Store in the refrigerator for months. Bring to room temperature before serving.