Panera is returning to the public markets after four years in private hands. St. Louis-based Panera Brands filed initial paperwork Tuesday for an IPO. It did not give a date or say how many shares will be offered. Restaurateur Danny Meyer, who developed the Shake Shack brand, said he will invest directly in Panera Brands at the time of the IPO and will become a lead independent director at the company once the IPO is complete. Panera was founded in 1987. It went private in 2017, when it was bought by JAB Holdings for $7 billion.