Sabrina’s offshoot Spencer ETA Burger is flipping patties for a good cause today. On a philanthropic tip, the University City burger joint is donating 20 percent of sales from today to Big Brothers Big Sisters Southeastern Pennsylvania. Each year the organization’s local branch struggles to raise $25,000 through the Bowl For Kids Sake campaign, but Spencer ETA Burger is pitching in, giving them a leg up on fundraising efforts. Just eight bucks gets you a burger, fries, and a beverage, and a chance to help them help out the community. Meanwhile over on South Street, Supper’s Mitch Prensky’s is serving slices of Boston Cream Pie, and turning over all the proceeds to The One Fund Boston to honor victims of last week’s Boston Marathon tragedy. The week-long effort begins tonight, and runs through next Tuesday.