Rinse apples, remove stems and blossoms, unpeel and cut into small pieces with the core. Place apple pieces in a wide saucepan, pour enough water to just cover. Heat the lemon peel, thinly peeled, until cooked, then remove. Do this until the apples have broken down.
Cool, put them in a juice cloth or a not too fine-meshed dish rag form and run the juice through, squeezing the juice bag a little at the end. Measure the juice and add sugar in a 1:1 ratio. Heat the juice with the sugar and continue boiling until a drop taken from the juice gels on a plate. Always skim the foam from the juice another time.
Variation with Calvados:
When the jelly is ready, fold in the Calvados, fill hot into jars and seal them on the spot.
Variation with rose petals:
Dip the rose petals briefly in boiling water, then quench in iced water. Drain on a dish rack and simmer in the jelly until they no longer float to the top. Add rose oil. Fill hot jelly into glasses and close them on the spot.