Place mint leaves in the cocktail shaker. Then, muddle them gently to release oils.
Add lime juice, orange juice, and simple syrup to the shaker.
Fill the shaker with ice cubes and shake for 10-15 seconds.
Fill a julep cup or tall glass with crushed ice.
Strain the mixture into the glass.
Top the drink with Sprite, then stir gently.
Garnish with an orange slice and a fresh mint sprig.
Notes
Keep mint leaves fresh by storing them wrapped in damp paper towels in the fridge.Make simple syrup ahead by mixing equal parts sugar and hot water until dissolved.The drink tastes best when served right away while the ice is fresh and Sprite is fizzy.For a sweeter version, add an extra 1/4 oz of simple syrup.Replace Sprite with ginger ale or lemon-lime seltzer for different flavor options.