Sherbet is the dictionary-recommended spelling for the frozen dessert made primarily of fruit juice, water, and sugar. The misspelled sherbert, which results from a common mispronunciation (sher-bert instead of sher-bit), appears often enough to have earned a spot in some dictionaries. But it is still not as widely accepted as sherbet, which more closely resembles the Turkish and Persian words from which the English term is derived.
Examples
The misspelling is common in all types of writing—for example:
… but I do that sitting on a massive brown beanbag with a brew and a sherbert Dib Dab. [Independent]
Some great things to do when stoned: eat a mango sherbert, walk in the woods, have sex, listen to Sigur Rà³s or Grizzly Bear … [Daily Caller]
Opened in 1988, the ice cream business has made its own ice cream, yogurt and sherbert all along … [The Day]
But most publications with high editorial standards spell sherbet in the conventional way—for example:
Sales of nostalgic sweets such as dip dabs, bon bons and sherbet fountains, have all leapt up over the last year … [Telegraph]
Jeans have gone from basic blues and intense indigo to Technicolor versions of playful sherbet shades. [Los Angeles Times]
Take a seat in the vintage, century-old lime-sherbet barber chairs and the conversation turns to all the commotion in the neighborhood the past few weeks. [San Francisco Chronicle]

