Add 4 mint leaves to a tall glass and top with two lemon slices. Muddle the mint and lemon to release the juice and oils. Repeat with remaining mint and lemon.
Divide the ice between the two glasses. Top the ice with 1 1/2 ounces gin, 1/2 cup lemonade and 1/4 cup club soda. Repeat with the remaining gin, lemonade and club soda. Stir to combine.
Garnish with blueberries, if desired and serve immediately.