Talk about learning from the bottom up.

Manhattan’s rookie DA, Cy Vance, spent yesterday morning in a misdemeanor courtroom, handling routine procedures like grand-jury votes in minor larcenies and plea deals for check forgers.

Vance’s court stint was part of an office-wide effort requiring senior prosecutors to pitch in one day a month to help cut a massive criminal court backlog that last year resulted in some 5,000 defendants being sprung under the state’s speedy-trial statute.

“If you run a major corporation, I think it’s important to understand what’s going on on the assembly line,” he explained.