In a medium-sized pot over medium heat, combine quince, sugar, lemon juice and water. Stir occasionally until the sugar dissolves.
Add the cognac once the sugar has dissolved.
Continue to simmer the mixture uncovered for approximately one hour, or until a candy thermometer reads 104°C/220°F. Perform a plate test to ensure readiness*.
Grease a 20cm/8” square baking dish. Purée the quince mixture until smooth.
Pour the purée into the dish, cool to room temperature, then refrigerate until firm.
Cut into squares for serving.
*To test for doneness, place a dollop of mixture onto a chilled plate. If it wrinkles and feels gel-like, it is ready.
The quince will turn a deep ruby red as it cooks.
If the paste is too thick after cooling, it can be slightly warmed to spread.
Store the squares of quince paste covered in the refrigerator for up to 3 months or freeze well-wrapped for up to a year.
