Blanch the apricots in boiling water. Remove the apricots from the water and peel. Cut in half, remove the stones, and finely dice. Rinse the lemon in hot water, finely grate the zest, and squeeze the juice. Mix the zest and the juice with the apricots and jam sugar in a large saucepan. Let infuse for 1 hour, until juice begins to form in the pan.
Bring to a boil, stirring constantly. Cook for 4 minutes, until the jam begins to thicken, then add the lavender flowers.
Fill the prepared jars to the brim with the jam. Seal tightly and cool completely.