1. Please see my top two recommendations for succeeding with this recipe in the body of the post. Both are very helpful -- the first, critical.
2. Although pretty in its Japanese aesthetic, I don't normally serve this meal in divided portions. In reality, the broccoli is mixed in with the meat and the sauce. I just wanted to do something different for the presentation.
3. I have found with cornstarch over the years that it really doesn't work well to mix it directly into a sauce. It's worth the extra minute dissolving it in water first before integrating it.
4. Although I have not tried it in this particular recipe, I often use tapioca flour as a thickening agent. So if you prefer to skip the cornstarch, this is another good option.