Mince onion and garlic. Cut carrots and broccoli according to your desired cut. Slice mushroom.

Slice beef sirloin into thin strips.

Then put oil in the pan with. Sautè onion till brown then add garlic. After sauteing add in the beef till its tender.

Then add oyster sauce and soy sauce in the pan. Let it simmer for 5 mins. Then add water. And let it simmer again for another 10 mins. Then we can add in the mushroom and carrots.

Then dilute the flour and cornstarch in water and if the meat is tender we can add the flour and cornstarch mixture to the pan. Dont let it be too thick. Just add water gradually till you reach the exact consistency of the sauce. Then we can add in the butter and broccoli and let it simmer a bit for 3 mins. Then its done!