Italian 9 around start of Christmas month depicted in book of twelve leaves (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

DUOMO (Italian word for 9a DOME) around DEC I (abbreviation for December 1 = start of the Christmas month). A book whose page size is derived from folding a standard printer’s sheet of paper into 12. (From duodecim , Latin for twelve.)