For the peach lavender jam, first wash the jars and lids hot and boil them. Turn them upside down and let them dry. Put them directly in the place where they will be filled (tray with cloth). Sort out the lavender flowers, but do not wash them.
Roll the lemon across the kitchen counter with the palm of your hand (yields more juice), cut in half and squeeze. Prepare the peaches (wash, blanch, skin, halve and pit) and cut into small pieces.
Mix the peaches, lemon juice, jelling sugar and lavender in a wide, high pot. Cover and allow to infuse for at least 4 hours. Stir occasionally.
Then boil until bubbly, about 4 minutes (follow directions on sugar package). Stir constantly to prevent peach lavender jam from burning.
Skim peach-lavender jam if necessary. Make a jelly test. For the jelly test, pour some jam onto a cold porcelain plate. If the jam gels, pour into jars.
Pour the peach lavender jam as hot as possible, to the brim, into the prepared jars and seal immediately. Place the jars upside down on a tray covered with a damp cloth for 6 minutes.
Then invert the jars again and let cool on the tray. Store in a dark and cool place.