Combine hamburger and onions in a large saucepan over medium-high heat and season with salt and pepper. Cook, stirring frequently, until hamburger is browned and onions are translucent, about 5-7 minutes.
Reduce heat to medium and add 3 cups of water and the Kitchen Accomplice Beef Broth Concentrate or Beef Bone Broth Concentrate, stirring to dissolve the concentrate. Bring liquid to a simmer.
Combine flour, 1/4 teaspoon salt, 1/4 teaspoon pepper and the remaining 1 cup of water in a container with a lid. Shake well, until mixture is free of lumps. Slowly add the flour-water mixture to the simmering stock, whisking constantly, until the gravy comes back to a simmer and reaches the desired consistency.
Add Worcestershire sauce to taste and simmer hamburger gravy for another 5 to 10 minutes, reducing the heat as needed to keep it just at a simmer. Season to taste with additional salt and pepper if necessary.