Taquiza's Steve Santana does more work than necessary. No one said he needed to import dried blue corn from small Mexican farms. Not a soul told him to undertake the painstaking process of turning it into cornflour and then making tortillas. No one demanded they be filled with the slightly spicy, charred poblano strips called rajas or the tangy corn fungus known as huitlacoche. Yet the programmer-turned-cook, who did stints with Jeremiah Bullfrog and at Giorgio Rapicavoli's Eating House, decided it had to be done. And that was the beginning of a little walk-up counter on Collins Avenue that set a new standard for excellent tacos in a city where tacos are booming.