Lightly wipe off the frying pan that was used for cooking the steak and pour in the mixture from Step 2. Bring it to a simmer over low heat (If the frying pan is still really hot, then you can also just take advantage of the residual heat).
Pour over the steak and enjoy.
Story Behind this Recipe
I really wanted to recreate the flavor of that standard Japanese-style steak sauce, so I thought of this.
This goes really well with beef steak, of course, but it also goes well with sautéed chicken, hamburger, basically any cooked meat!
Be careful not to let the sauce simmer for too long, since you don't want to lose the flavor of the onions. It's best to cook it just until the bitterness is gone.
If you end up evaporating off too much of the liquid, you can try drizzling on some ponzu when plating.