+1. Low sodium chicken stock (especially homemade) is magic and adds "love" or scratch made flavor to anything it touches. Probably the best hack there is. Butter also works but be careful with compounds as most store stuff is already loaded with salt.
I'd hit the the gravy with some fresh ground white pepper. I like orange zest and chili powder on yams. Maybe some nutmeg too.
FYI my MIL ran Yacht Club and Elks Club kitchens and stellar cook. Blew my mind talking shop with her. Very little scratch made in commercial kitchens. It's all about tweaks like stock and spices.
I make my own compound butter, and always use unsalted butter. I don't want a company controlling my seasoning profile! :)
As for yams/sweet potatoes, this is my recipe that my wife loves (I don't mash, but use a food processor to make them very smooth and creamy):
Ingredients
5 sweet potatoes
1/4 teaspoon salt
1/4 cup butter
2 eggs
1 teaspoon vanilla extract
1/2 teaspoon ground cinnamon
1/2 cup white sugar
2 tablespoons heavy cream
1/4 cup butter, softened
3 tablespoons all-purpose flour
3/4 cup packed light brown sugar
1/2 cup chopped pecans
Directions
1. Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x13 inch baking dish.
2. Bake sweet potatoes 35 minutes in the preheated oven, or until they begin to soften. Cool slightly, peel, and mash.
3. In a large bowl, mix the mashed sweet potatoes, salt, 1/4 cup butter, eggs, vanilla extract, cinnamon, sugar, and heavy cream. Transfer to the prepared baking dish.
4. In a medium bowl, combine 1/4 cup butter, flour, brown sugar, and chopped pecans. Mix with a pastry blender or your fingers to the consistency of course meal. Sprinkle over the sweet potato mixture.
5. Bake 30 minutes in the preheated oven, until topping is crisp and lightly browned.