This recipe is very simple, but it takes a tiny bit of an effort, as you need to do the prep the night before cooking. This is because the pumpkin needs to rest 12 hours after having been mixed with the sugar. So, the best is to pick an evening you have no plans for and start on it, then finish it the following day.
Take your pumpkin, peel it, remove all seeds and dice it. Place it in a large saucepan and mix in the sugar. Put a lid on it and let it rest for the night in a cool place. Once this time has passed, you can finally turn on the stove and make your jam. Put the saucepan on low heat and add the juice and rind of the lemon (better if it is organic, as you need to use the rind), the cinnamon and the nutmeg. Cook, always on low heat, for about an hour. Remove the lemon rind and, if you would like your jam to have a very smooth finish, sieve it. This done, add the amaretto and stir very well.
While your jam was cooking you should have gotten your mits on a few mason jars, of course: now it is time to use them! Place the jam immediately in the jars, close and turn them upside down. Let them cool, then place them in a large saucepan and cover with cold water. Bring to the boil and let the jars boil for 20 to 25 minutes. Turn off your stove and let the water and jars cool before handling them.