For the fennel espuma, rinse the fennel and cut into pieces. Heat the olive oil in a pot and sauté the shallot with the fennel.
Deglaze with Pernod, add water and cook for another 15 minutes possibly together with the fennel seeds.
Blend in a hand blender with the fennel greens and pass through a fine sieve.
Squeeze out the gelatin soaked in cold water, let it melt in the still warm puree and season strongly with salt and freshly ground pepper.
Refrigerate, whisk and pass through a sieve again. Pour the mixture into the iSi Gourmet Whip, seal and press lever.
Serve the fennel espuma with smoked salmon, if desired.