Bring a large pot of water to a boil; add beef tips. Boil beef tips until thoroughly cooked, about 15 minutes; drain.
Transfer beef tips to a skillet over medium high heat. Add butter and onion; cook and stir until onion is very tender and dark brown, about 10 minutes. Stir in Worcestershire sauce and red pepper flakes; cook until liquid is absorbed, about 5 minutes. Cook and stir meat mixture until well coated and shiny black, 1 to 3 minutes more.