Place washed celery leaves and stalks into a slow oven for about 2-3 hours. (Approx 100ºC) They should be dry and crispy but still green when they are ready.
Dry toast fennel seeds on Induction 10 for a few seconds until fragrant and popping.
Place all the leaves, the fennel seeds and the salt into Thermo bowl and blend 8 sec/speed 5-8.Place into airtight dry jar. Will keep indefinitely. The range of speed is larger than I like, but it will really depend on the size of the salt crystals you end up using.