Portillo’s is a fast-casual restaurant chain considered a one-stop shop for iconic Chicago foods. Founded in 1963 in the Southwest suburbs of Chicago, Portillo’s is known across the country for its hot dogs, Italian beef sandwiches, cheese fries, and chopped salads. But its best kept secret is the restaurant’s cake shake. Insider's Medha Imam visited Portillo’s Summit, IL location to learn what goes into making the iconic cake shake. Rumor has it they put an entire slice of chocolate cake into their milkshake, making it a must-try dessert.