Beef Gyudon

We've been having chicken for two days already and it's time to have a beef break!  I cooked this Gyudon for dinner, to Brandon's delight :) 
I got the recipe from Recipe Zaar web-site, that I tweaked a bit to our liking.  I used Australian Beef Tenderloin instead of the usual sirloin or sukiyaki cut for Gyudon.

Ingredients:
Approximately 500g of Australian Beef Tenderloin, cut into cubes
1 whole white onion, cut into big strips
1/2 cup water
1/4 cup mirin
1/4 cup Kikkoman soy sauce

Procedure:
Combine water, mirin and soy sauce in a sauce pot and let it boil.
Add the onions, and cook until half-cooked.
Add the beef and cook for about 3 minutes or until medium well.  (Overcooking your beef will make it tough, so be careful.)
Put on top of hot rice and serve to your hungry husband!!! Hahaha!