How do I make beef for stew soft?

I made a stew yesterday, but I didn’t put in enough beef. I want to add more today, but I don’t want to add it to the stew and have to cook it again.

I want to be cook the beef separately and then add it to the stew after it is cooked. How can I do this and have each chunk of beef nice and soft.

I was thinking I would fry the beef chunks on high heat and get a nice sear on the outside. The inside would still be raw. After I would put it in a pot of water and soy sauce on the lowest heat and cook it for 15minutes. Then just let it sit. Will this be sufficient?

Don’t worry about the flavor. I’ll take care of that. I just want to know hot to make the beef melt in your mouth tender.