Add prepared quinces and water to a large Dutch oven. Cover the surface with a piece of parchment paper that has been cut to fit.

Bring the water to a boil over medium-high heat. When the water starts to boil, reduce heat to medium-low and simmer for 1 1/2 hours or until the quinces can be easily pierced with a knife.

Place a colander over a large bowl and drain the quinces, reserving the cooking liquid (there should be about 5 cups)

Transfer the cooking liquid back to the Dutch oven. Bring the liquid to a boil and reduce to 3 cups (this will take about 15 minutes).

While the cooking liquid is reducing, blitz the cooked quinces in a food processor until very smooth.

Place a fine-mesh sieve over a bowl and press the puréed quinces through the sieve into the bowl. Work in small batches during this step, you should be left with 4 cups of silky quince purée. Discard the remaining solids.

Preheat oven to 350° F. Position oven wrack in the middle.

Grease 8x8-inch baking pan and line with parchment paper.

Pour quince purée back into the Dutch oven with the reduced cooking liquid. Add sugar and lemon juice, stir. Bring mixture to a boil.

Reduce heat to medium-low and simmer, stirring occasionally. After about 30 minutes, the mixture will have thickened and darkened in color.

Move the Dutch oven into the oven, placing it on the middle rack.

Cook the quince mixture for 1-1 1/2 hours, stirring and scraping the sides every 15 minutes. The finished quince paste will have thickened significantly and will have turned a vivid shade of plum red.

Using a spatula, carefully scrape the thickened quince paste into the prepared baking pan. Let it come to room temperature.

Transfer the quince paste to the fridge and let it set for at least 4 hours.

Flip the baking pan and its contents onto a cutting board, and remove the parchment paper.

Using a sharp chef's knife, cut the quince paste into smaller portions.

Wrap each slice in parchment paper and an outer layer of plastic wrap.

Store wrapped-up quince in the fridge for up to 6 months.