Heat oven to 400°. Place squash cut side down on a rimmed baking sheet. Roast until tender, 35 to 45 minutes. Cool slightly, then scrape the flesh into a blender or food processor and puree until smooth. Transfer the mixture to a saucepan and stir in the cider, brown sugar, cinnamon, cloves and salt. Simmer gently until thickened, about 20 minutes. Stir in lemon juice, cool and store in a clean sterilized jar or in an airtight plastic container, where it will keep for up to two weeks.