In a blender, pulse 1 cup mango and 6 mint leaves until roughly pureed.
Fill a cocktail shaker with ice. Add the mango puree, 2 ounces white rum, 1/4 cup simple syrup, and 2 tablespoons lime juice. Secure the lid and shake vigorously for 30 seconds until chilled.
Strain into two Collins glasses filled with ice. Fill each glass with about 6 ounces club soda, and then give a gentle stir.
Garnish with mint sprigs and extra mango pieces on a cocktail pick. Serve immediately.
Notes
Mango: Use fresh mango or thawed frozen mango chunks.Mocktail option: Leave out the rum and add extra club soda to taste.Pitcher option: Scale up the ingredients, and add club soda to each glass just before serving.Sweetness tip: If your mango is very sweet, use a little less simple syrup.