Place the fresh blueberries and thyme leaves into a mixing glass.
Use a muddler or the back of a spoon to gently crush the blueberries, releasing their juices and infusing the thyme flavor.
Pour in the gin, lemon juice, and simple syrup.
Add a generous amount of ice to the mixing glass and stir well for about 30 seconds to chill the mixture thoroughly.
Strain the concoction into a tall glass filled with fresh ice.
Carefully pour sparkling water over the top to create a refreshing fizz.
Adorn your drink with a few whole blueberries and a sprig of thyme for a beautiful presentation.
Enjoy your delightful sparkler!