Combine all the marinade ingredients in a large pan. Bring to a boil.
Let the sauce mixture simmer for five minutes. Remove from the heat.
Cut the steak into small pieces and transfer them to a ziplock bag.
Pour the now-cooled marinade over it.
Marinade the steak for between 12-24 hours.
Once that is done, heat the oil and melt the butter in a pan.
Add the onions, salt and pepper, and sugar. Cook for half an hour.
In the meantime, drain the excess liquid from the steak and transfer it into a pan.
Cooking the steak for approximately three minutes per side would result in a medium-rare steak. Cook according to your preference.
Serve with the caramelized onion, along with side dishes of your preference.