Early life and family
Tosi was born in Ohio and raised primarily in Springfield, Virginia to an agricultural economist father of Italian origin and to an accountant mother. After studying to become an electrical engineer for one year at the University of Virginia, she spent time in Florence, Tuscany, Italy, to see if she wanted to be a translator. Eventually, she graduated from James Madison University. After graduating, she moved to New York and enrolled in the French Culinary Institute's pastry arts program.
On July 30, 2016, Tosi married New York City-based restaurateur Will Guidara.
Tosi entered the culinary field at the fine dining restaurant, Bouley, and then advanced to wd~50. In 2005, she helped to write wd~50’s Hazard Analysis Critical Control Point plan.
On the recommendation of Wylie Dufresne, David Chang hired Tosi in 2005 at Momofuku to write his food safety plans and help administratively with the NYC Department of Health. Chang was so impressed with Tosi that he hired her to run their pastry program. There were no desserts on Chang's menu when Tosi came on board, and she created her own pastries, putting her extreme spin on childhood favorites, from cereal-milk panna cotta to fried apple pies with sour-cream ice cream and toasted miso.
In 2008, Momofuku Ssam Bar's adjoining next store space became available, and Chang encouraged Tosi to open her own shop, which she named Milk Bar. She had free rein to develop new recipes and the menu soon featured her trademarked Cereal Milk, Compost Cookies, Crack Pie and Candy Bar Pie. In December 2009, Anderson Cooper appeared on Regis and Kelly professing his love for Milk Bar and its Crack Pie.
By 2012, Milk Bar had grown from one retail sales location in the East Village of Manhattan to nine retail outlets in New York City, one in Toronto, Canada (opened in 2013), three in Washington, D.C. (opened in October 2015, February 2018 and May 2018) one in Las Vegas, Nevada, at the Cosmopolitan of Las Vegas (opened in December 2016), and one in Los Angeles on Melrose Avenue (opened in September 2018). Tosi opened her first Boston-area store in Harvard Square in Cambridge, Massachusetts, in a unique partnership with &pizza, a Washington D.C.-based pizzeria chain. The Boston store was Tosi's 16th Milk Bar, and by February 2019, Milk Bar employed 381 people across North America.
As a judge on MasterChef, Christina acts as the right-hand woman while judging. She holds the same high standards as Ramsay and would often be irritated by the contestants' constant mistakes. While she is more subdued than Ramsay, she has her own limits when pushed, would lash out at any disrespectful contestant. Unlike Ramsay, Graham, or Joe, she has a very passive-aggressive behavior. On one hand, she appears as nice and friendly on the outside. On the other hand, she can become stern when the contestants aren't taking the competition seriously and her criticisms can be considered to be either slightly or overly harsh, sometimes even going as far as taking a contestant's poor performance personally as an insult and berating them for their mistakes. Despite this, she is calm and friendly both inside and outside the kitchen and would let the contestants know when they have done well.