What is the best way to make a flavorful gravy using broth or stock as the base?

To make a flavorful gravy using broth or stock as the base, start by making a roux with equal parts fat and flour. Cook the roux until it turns a light golden color, then slowly whisk in the broth or stock. Simmer the mixture until it thickens to your desired consistency, then season with salt, pepper, and any herbs or spices you like. Adjust the seasoning as needed and serve hot.