Core each apple (do not peel!) and cut into about 6 pieces. Add the apples, frozen raspberries (thawed or frozen), apple juice, if using, and lemon juice to a large pot. Bring to a boil and continue to simmer, partially covered, for about 30 minutes. Remove the lid and simmer for another 10.

Remove from the heat and let cool for about 20 minutes and then use an immersion blender to puree it. Cool and store in the fridge for up to 4 days. Freeze any leftovers after that.