- Prepare 2 or 3 1lb-jars and lids by washing well in warm soapy water and rinsing thoroughly. Bath them in a pan of boiling water for a while. Dry the jars.
- Wash the lemons and dry them up. Remove yellow part of peel from lemons in strips with a sharp vegetable peeler and slice them into 3-cm strips. With knife, tip off the pips and cut off all white membrane, or pith, from peeled lemons and discard. Cut peeled lemons crosswise into 1/3-inch-thick slices. Peel and core the apples. Cut them into small dices.
- In a big non-aluminum pan, add the prepared fruits and the preserving sugar and combine them briefly. Cover and refrigerate 3 to 4 hours. You would see a lot of liquid coming off the fruits. Heat lemon mixture to boiling over medium heat, and allow it to boil for about 5 minutes, stirring frequently. Ladle marmalade into still very warm jars to prevent the jars from cracking when the hot filling is added. Wipe jar rims clean. Seal with lids and bands. Store marmalade in cool, dry place. After opening jar, store marmalade in the refrigerator.