In a large glass or cocktail shaker, muddle the blueberries and mint leaves with a muddler or the back of a wooden spoon until the berries are broken down and fragrant.

Add the lemon juice, chia seeds, and honey (if using). Stir to combine.

Pour in the cold water and stir well. Let it sit for 5 minutes to allow the chia seeds to hydrate slightly.

Fill two glasses with ice cubes and divide the blueberry mixture evenly between them.

Top each glass with sparkling water and give it a gentle stir.

Garnish with extra mint leaves and a few whole blueberries if desired. Serve immediately.