An auction to sell off Upper Crust’s assets, including leases for 10 bankrupt stores, is scheduled for Dec. 19 at the Hilton Boston Logan Airport. More than 60 parties — including national brands and small businesses — have expressed interest in making a bid for the gourmet pizza company, according to Mark G. DeGiacomo, the trustee overseeing the bankruptcy of the Boston-based chain. Investors can bid on individual locations, as well as multiple stores and related assets, or the entire business, DeGiacomo said. Last month, he closed the bankrupt stores and laid off 140 workers because Upper Crust, which has faced years of labor troubles, had just four days of supplies and only $14,000 in cash after company officials paid themselves a month’s salary in advance. Founder Jordan Tobins, who was placed on leave earlier this year by Upper Crust’s co-owners after they accused him of misusing corporate funds, has said he’s interested in buying back the pizza chain with new partners. Tobins currently operates two Upper Crust locations that are not part of the bankruptcy — in Beacon Hill and Brookline.