If the rationalist deduces what is logical based on their empirical experience then their reasoning is flawed. We have to accept the axiomatic truth that our senses are limited and cannot account for an absolute truth.

To separate valid perceptions from invalid ones, a person first must assume that the world can be known through the senses. They must also assume that the world is objectively real. These assumptions do not get along well with one other. To say the world is objectively real is to say it is independent of and indifferent to sense perception. Then what in the world can we know? We can know only the effects of the parmesan cheese upon our senses, not the cheese itself.

If all knowledge is empirical, you have your solution already. Just make an experiment. Use a heuristic to estimate an amount, test it and adjust as you go.

I see that the chef is of the same I Always Want More school of parmesan as Ben Lapidus and Heidi Klum.