For those seeking more modest, relaxed surroundings, Patisserie Tomoko, a half-bakery, half-dessert bar, opened in Williamsburg, Brooklyn, in November with a dessert prix fixe ($12 to $16) available at a counter beneath space-age lamps. The pastry chef and owner, Tomoko Kato, is still settling in, and only a few desserts are available on any given day. But there is promise here, in a cake of rich chestnut mousse undercut by bracing pear gelée and in the terrifically soft matcha cookies that have the texture of a half-baked brownie.