Decorative Grooving on Pie or Flan Tins
Puzzle 10 of City Nicknames Hard Pack
Question is: Decorative Grooving on Pie or Flan Tins
and the answer is: FLUTING
Word Meaning:
FLUTING — (architecture, sculpture) A decoration consisting of parallel, normally vertical, flutes (grooves) incised into the surface.
Definitions from Wiktionary.