Pie-making material? (3)
I believe the answer is:
mud
'material?' is the definition.
(mud is a kind of material)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for mud that I've seen before include "Offensive remarks" , "slander" , "Sludge" , "In your eye, this is an informal toast" , "Soft wet earth" .)