By Elyssa Goodman In the middle of New York’s bustling midtown, there is, of all things, a 6½ Avenue. And on that 6½ Avenue, nestled between West 53rd and West 54th Streets, is a tiny enclave so small and quiet that for a few hours in its wood-lined walls, New York disappears completely. With a mere 20 seats, Kaiseki Room by Yamada is a respite from the whir of the subway and the honking of taxicabs, a moment of zen delivered via Japanese cuisine in its highest, most meticulously crafted form. For the uninitiated, kaiseki is an elegant, centuries-old tradition in the Japanese culinary world, a…