This tight but artsy little jewel box of a restaurant, courtesy of Ravi DeRossi, aims to give vegan food some well-deserved polish. Avant Garden’s dynamic menu couldn’t have arrived at a better time, as New York diners are hungry for more upscale meatless options. This is excellent food that just happens to be vegan.Try the cold, salt-baked sweet potato with puréed watercress, crispy jicama and Meyer lemon; or deep-fried sushi rice topped with avocado, smashed ginger, sesame seeds, and streaks of miso paste. Sheets of pasta are tossed with pesto, tomatoes, haricot verts, and Kalamata olives. Their thick slices of toast topped with cremini mushrooms, sweet onion marmalade, toasted walnuts, and herbes de Provence are destined to become a signature item.