Brussels sprout is indeed a vegetable name that is commonly misspelled. The incorrect spelling "Brussel sprout" is a frequent mistake as people do not anticipate the first word having an "s". However, the correct spelling includes the plural form "Brussels" to indicate that the vegetable is named after the region where it was first cultivated, which is believed to be near Brussels. Even if you are only speaking about (1) tiny cabbage, you would still say "Brussels sprout."   To complicate matters further, the "B" is always capitalized as well.
While Brussels sprout is a frequently misspelled vegetable name, there are other vegetables with names that can also be challenging to spell, depending on an individual's familiarity with them. Some examples include eggplant/aubergine, zucchini/courgette, cauliflower, and asparagus. Spelling can vary regionally and across different English-speaking countries, adding to the potential for confusion.