The ever-busy Joanne Chang has plenty of reasons to celebrate. Her Flour Bakery + Cafe empire continues to expand; she opened a fourth location on Clarendon Street in the Back Bay on Jan. 11. Her second book, “Flour Too,” is due out in May, featuring recipes for the cafe’s sandwiches, soups, salads, and various specials. And as she gets ready to ring in the Lunar New Year on Feb. 10 at Myers + Chang, the pan-Asian restaurant she operates with her husband, Christopher Myers, Chang, 43, reflected on her latest projects and on past holiday celebrations growing up in a Taiwanese family in Houston, Denver, Tulsa, Okla., and Dallas.