Prepare jars, lids and boiling water bath. Combine the liqueur, water and sugar in a pan and cook over med-high heat, stirring frequently, until sugar is dissolved and mixture has coem to boil. Remove from heat. Pick over, wash and dry blueberries, then pack them in hot dry jars, placing 4 lavender flower heads in each jar. Leave 1 cm headspace. Pour hot liquid into jars, just covering berries. Wipe rims with clean towel and attach lids securely. Place jars in boiling water bath, and when water returns to full boil, process for 15 mins.