Quince fruit leather cut into blocks is a classic Mexican confection. This family-friendly treat is a sweet, firm, aromatic candy traditionally served with manchego cheese.
Wash quinces thoroughly, then cut into quarters without peeling or coring. Place them in a large pot with 4 cups water.
Bring to a boil over medium-high heat, reduce to a simmer, and cook covered for 40–50 minutes until quinces are soft and fragrant.
Drain and cool slightly. Pass the soft quinces through a food mill or fine-mesh sieve to remove skins and seeds, creating a smooth purée.
Return the quince purée to the pot. Stir in sugar and lemon juice. Cook over medium-low heat, stirring continuously, for 1–2 hours until the paste turns deep orange-red and thickens to a moundable consistency.
Line a baking dish with parchment. Spread the cooked paste evenly to about 1-inch thickness. Let cool, then air-dry uncovered at room temperature for at least 4 hours or overnight until set and sliceable.