Add ingredients (except soda) to a cocktail shaker.
Fill the shaker with ice and shake well.
Strain out ice into another shaker or glass and shake again without, ice making a stiff foam.
Pour into a Collins glass or large stemless Champagne glass.
Submerge cocktail spoon into glass gently — avoid stirring or disturbing foam.
Then, pour lemon soda down the spoon so as not to disturb the foam. The foam should rise just above the rim of the glass.
Remove the bar spoon and garnish with green nasturtium flower and lemon.