A young Guide making a chocolate treat (7)

I believe the answer is:

brownie

I'm a little stuck... Click here to teach me more about this clue!

'chocolate treat' is the definition.
(I've seen this in another clue)

I don't understand the rest of the clue.

(Other definitions for brownie that I've seen before include "Junior Girl Scout" , "fattening food" , "confection" , "nutty cake" , "Chocolate cake; elf" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.