Add all ingredients except soda water to a cocktail shaker with ice and vigorously shake until chilled. Strain back into the cocktail shaker, discard the ice, and shake again (reverse dry shake). Double strain into a chilled Collins glass. Top with soda water until soda reaches the brim of the glass. Let drink sit for 2 minutes and top with more soda water to create a foam head. Garnish with a mint sprig.