Make roux: Melt butter over medium heat. Add flour, whisk constantly 2-3 minutes until light golden and nutty.
Add broths: Slowly pour in chicken broth while whisking constantly. Add beef broth, continuing to whisk until smooth.
Season: Whisk in soy sauce, brown sugar, Worcestershire, garlic powder, onion powder, pepper, MSG, and ginger. Stir until sugar dissolves.
Simmer: Bring to gentle simmer. Reduce heat to low, simmer 8-10 minutes, stirring occasionally, until thickened.
Adjust: If too thick, add broth 1 tablespoon at a time. If too thin, simmer longer or add cornstarch slurry.
Season: Taste and adjust salt as needed. Strain through fine-mesh strainer if desired for ultra-smooth texture.
Serve: Serve hot over fried chicken, rice, or potatoes.