Dont be fooled by my grandiloquence
look past the words to find my substance
Just distraction? "Look past the words" meaning the words in these two lines?
Past my skin if you shall pry
my prominent brother will make you cry
"My prominent brother" is the onion. You cry if you open a shallot or onion.
I am almost shallow but dont confuse
Utilise my extract to infuse
"Almost shallow" is a nice bit of wordplay: 'shallot' and 'shallow' are only one letter different. Not sure about the next line: can shallot extract be used for something?
Your boiling, frying if allotment you find
Contain your grief, compose and grind
You can boil or fry shallots, or grow them in an allotment (which is another bit of wordplay: 'shallot' and 'allotment'). If you can stop crying after peeling a shallot, you can then grind it.