Identify how you use Locatelli: topping/grating, pasta sauce, or gratin/baking—this determines whether you prioritize crumble vs. melt.
Pick the closest flavor axis: nutty hard Italian (Parmesan/Grana) or salt-forward aged sheep (Pecorino Romano).
Swap by the listed ratio (usually 1:1). If the substitute is saltier (Pecorino Romano), start with slightly less and taste.
For topping/grating, grate fresh; for baked/gratin use, spread evenly so it browns instead of clumping.
Adjust after the first taste: add a pinch of salt only if the substitute is mild, or add acid/sweet (lemon zest or a tiny pinch of sugar) if it’s too sharp.