Make the simple syrup by combining water, sugar, and dried lavender in a small saucepan. Add in the frozen blueberries if you'd like to color the syrup purple. Heat over medium, and stir until sugar is melted. This will take about 2 minutes—the liquid should just start to simmer.
Turn off the heat, and let the syrup sit for 1 hour. Strain into a liquid measuring cup or jar for storage.
Chill until cold.
To make the lavender lemonade, pour ¼ cup lavender syrup and ¼ cup lemon juice into a small pitcher, then pour in water. Stir well to combine.
Fill two glasses with ice and a lemon slice (if desired), then pour in the lemonade.
Notes
Storage Tips: This lavender drink is easy to make in advance. You can either store the lemon juice and lavender syrup in separate containers in the refrigerator or make the full drink (minus the ice) and store it. The syrup will last for several weeks. Lemon juice or the combined lavender lemonade will be best within 3 days, but will last up to a week. Expert Tips: If you want to make a larger batch for a party, double or triple the recipe as needed. This recipe makes more lavender syrup than you will need for 2 drinks anyway, so you will have plenty to make a larger batch. If you make it ahead of time, see Storage Tips above.