We've sung the praises of the City Bakery's Maury Rubin so often in the past —- for his luscious and imaginative lemonades, his perfect croissants, his tarts, his sweets, his revolutionary salad bar, even his oatmeal and his homemade marshmallows —- that we fight the urge to bestow still another gushing tribute. But chocolate may be Rubin's greatest achievement yet. This isn't to take anything away from the city's elegant luxury chocolatiers who smuggle their precious, fresh confections in daily from France, Belgium, and Switzerland: La Maison du Chocolat (1018 Madison Avenue, between 78th and 79th Streets; 744-7117), serving a Willy Wonka–worthy river of molten hot chocolate in its new, enlarged boutique, Richart (7 East 55th Street; 800-richart), with its Harry Winston–esque display of gemlike bonbons; and Teuscher’s (25 East 61st Street, 751-8482; Rockefeller Center, 246-4416) insurmountable champagne truffles. Nor is it to detract from the community of talented American and French pastry chefs whose shared goal is to drown the dining public in a sea of flourless, oozing chocolate-soufflé cake. (Not that we’re complaining, mind you.) But not all chocolate cravings call for haute fixes. Often, what we want is something slightly less sophisticated and more fun —- a milk-and-cookies regression. To satisfy our grown-up snacking urges, no one approaches the evolving chocolate repertoire at Rubin's City Bakery (22 East 17th Street; 366-1414). Milky Way tarts, perfectly textured brownies, and dense double-chocolate cookies with chunks of white chocolate —- an abomination to most chocoholics but strangely alluring here —- beckon irresistibly from their point-of-purchase position on the checkout line. And it's easier to survive winter knowing that come February, the hot-chocolate festival returns with exotically flavored variations on the melted-Valrhona-and-cream theme. Since chocolate and its addiction know no season, rejoice that in summer the same brilliantly doctored concoction is served over ice.