Can use more juice, but need at least the 2 cups. Add to a hot (cast iron is best) skillet on a medium high temperature.
Add the salt and pepper, stir with whisk and keep heat up to med. high. When the juice, (drippings) begin to carmelize, add the cornstarch. If not enough, add more. When it begins to thicken up, don't add anymore.
Be sure to keep stirring with the whisk and as it thickens up, then turn off the stovetop, keep stirring a few more minutes.
Ladle over potatoes, chicken, rice, etc Top with cut up green onions.