31-inch slices of lemon zest, with all the white pith removed
1 1/2cupsvanilla sugar (or the same amount of sugar with 1/4 teaspoon vanilla extract added)
3cupswhite wine vinegar,or cider vinegar
Cut the fennel bulbs into large chunks. Make them whatever size you want, but trim any edges that are very thin -- and remember people will eat these by the piece, so cut accordingly.
Bring the sugar, salt and vinegar to a boil. It should be tasty. If it is too sour, you can add a little water, but not more than 1/2 cup. Add the lemon zest. Once the canner is boiling, add the fennel pieces to the vinegar mixture, cover it and turn off the heat. Let it steep for 5 minutes.
In the clean jar, wrap the fennel fronds into the bottom so they surround it like a nest. Pack in the fennel pieces on top of the fronds; you want the fennel to come up only to the fill line on the jar (roughly the base of the neck). Pour in the vinegar mixture slowly, rotating the jar on the countertop to release air bubbles. Pour enough to cover the fennel by at least a 1/2 inch. Use a butter knife or chopstick to remove any stray air bubbles.
Seal the jar and process in the canner (water should be between 200F and boiling) for 15 minutes. Let it stand to cool on a rack.