score:1
It looks like "Fig. 128. Mitre, XII Century" in Herbert Norris, Church Vestments: Their Origin and Development (1950), ch. 9 "The Mitre":
ibid. "Fig. 133. Diagram of Triangular Mitre" and "Fig. 134. The Mitre more fully Developed" gives a pattern which could perhaps be adapted to a 12th cen. mitre: