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1
Split each roll along its equator with a serrated knife, opening it just enough to access the hollow interior without fully separating the halves. The cut face of the crumb should show the characteristic cavity of the rosetta or the dense inner channel of the ciriola. The crust must resist pressure and hold its shape.
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2
Drizzle the olive oil directly onto the exposed interior crumb of both halves, distributing it across the surface so it lubricates the bread before the filling is placed. This is the step on which the sandwich lives or dies: oil added after the filling pools rather than penetrating, and the bread remains dry at its core while the filling slides.
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3
Lay the mortadella slices into the lower half, folding loosely so the thickness holds volume rather than lying flat. The slices, cut at 3–4 mm, should build a layer with structural presence — not a compressed sheet. If white wine vinegar is used, apply a few drops directly onto the mortadella now.
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4
Place the Pecorino Romano slices over the mortadella, covering the surface evenly. The sharpness and salinity of the cheese must be present in every bite alongside the fat of the mortadella — uneven coverage defeats this balance.
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5
Close the roll and press gently. Eat within ten minutes of assembly: the rosetta's crust will begin to soften beyond its characteristic crispness after this point, and the hollow steam pocket — which moderates the interior texture — will be lost. The sandwich is ready when the exterior still resists the hand and the interior yields.