I am making a gravy for mashed potatoes. Looking at recipes online, I have found that a few of them don't require any butter, while others use them to varying ratios (to broth/water)
What is the role of this ingredient in an excellent gravy for mashed potatoes?
I thought of two:
Fat. Butter is rich in fat, and the increased fat in gravy helps it to coat and stick to the starchy molecules of the potatoes better, so they come together better in each bite.
Thickening. The oil in butter and the broth used in most gravy come together as an emulsion of sorts, like the way mayonnaise is made. This helps to thicken the gravy.