I haven't tried it in the slow cooker but I think it will work. Make the sauce and brown the meat and veggies first and then combine everything in the slow cooker. Cook it on low until the beef is tender (at least 6 to 8 hours). Add the masa and then let it cook a little longer to thicken. If the chili is not thick enough, just leave the slow cooker lid off to allow steam to escape before you serve it.