Recipe(tried): roux

When I do my roux, I use equal parts of butter and flour. For example, 2 tablespoons of butter and 2 tablespoons of flour. Melt the butter, then add the flour. The longer you cook it the darker it will be in color. The intensity of color will determine the taste.
I've also done a mock roux with chicken broth and cornstarch. Same measurements. While this still works to thicken, the taste isn't the same and you don't get the color or flavor intensity. BUT...you don't have the fat either.