Heat the oven to 200 C / 400 F with a rack in the center. Line a 33 x 46 cm / 13 x 18 inch sheet pan with parchment and tear off a second sheet of the same size for batch two.
Toss the grated Parmigiano-Reggiano, chopped rosemary and pepper in a small bowl until the rosemary is spread evenly through the cheese.
Scoop 8 heaped tablespoons of the mix (about 7 g each) onto the lined pan, leaving about 3 cm / 1 1/4 inches between them. Pat each into a thin, loose round about 6 cm / 2.5 inches wide.
Bake for 5 to 6 minutes, until the rounds are light golden and the bubbling has slowed. Check at 5 minutes, since they darken fast.
Slide the parchment with the first batch onto a wire rack. Lay the second parchment sheet on the pan, mound the remaining cheese the same way, and bake for 5 to 6 minutes.
Let all the crisps cool on the rack for 5 minutes. They look slightly soft when they come out and snap as they cool.