Peel, core, and chop quince into 2.5cm / 1-inch chunks. Place the quince into a large heavy-based saucepan full of water as you chop.
Bring to the boil then reduce to a simmer. Leave to cook for about 30 minutes or until the quince are soft when pierced with a knife.
Strain off the water then transfer the cooked quince to a blender and blend very briefly until a smooth paste forms.
Measure out the amount of puree you have then pour it back into your pot. Now measure out 3/4 of that amount in honey. Add that to the pot too, along with the lemon juice. (see note 1)
Place the pot back over a low heat and leave the quince paste to reduce for 2 - 2.5 hours with the lid off. Stir frequently to ensure it doesn't burn. It will eventually become more difficult to stir, and a wooden spoon will stand straight up in it without falling. The colour will also be a gorgeous shade of dark pink/salmon. (see note 2)
Line a 15 x 15cm (~6.5 x 6.5 inch) square dish with baking paper, pour in the cooked quince puree, smooth it out and leave to set in the fridge for a couple of hours.
You can either store in an airtight container and cut pieces as you need them or cut into squares in advance then store in the container. It keeps best if you place a piece of baking paper between each square/slice, so they don't stick. It will store for many months.