Put dried lavender in a spice or coffee grinder and grind flowers into a fine powder. Transfer to small bowl.
Whisk sugar, black currant powder, salt, and soy lecithin (if using) into ground lavender.
Transfer mixture back to grinder (you may have to work in batches) and process until entire mixture is a fine powder.
Store lavender powder in an airtight container at room temperature until ready to use.