little by little

pikkuhiljaa, pala palalta, pikku hiljaa

hiljalleen A small amount at a time.
1861, w:Charles Dickens|Charles Dickens, Great Expectations, ch. 59:

Everything else has gone from me, little by little, but I have kept this.

Little by little his head cleared, and he began once more to take a personal interest in the battle.

Iraq's government has been removing blast walls little by little since late 2008, trying to restore a semblance of normalcy to this bunker city.