Syrupy substance produced by Missouri girls (8)
I believe the answer is:
molasses
'syrupy substance' is the definition.
'molasses' can be an answer for 'substance' (molasses is a kind of substance). I am not sure about the 'syrupy' bit.
'by missouri girls' is the wordplay.
'by' is a charade indicator (letters next to each other).
'missouri' becomes 'mo' (abbreviation for the US state).
'girls' becomes 'lasses' (lass can informally mean a girl).
'mo' put next to 'lasses' is 'MOLASSES'.
'produced' acts as a link.
Can you help me to learn more?
(Other definitions for molasses that I've seen before include "What's sweet" , "Black treacle" , "Thick treacle left over after refining raw sugar" , "Thick dark syrup made from sugar cane" , "Slow runner" .)