Peel and cut potatoes. Boil 20 minutes until fork tender. Mash with hand mixer. Add salt and pepper, to taste.
To make mushroom gravy: In saucepan over medium heat, brown butter and flour. Once butter is paste-like, add mushrooms. Whisk in chicken broth and heavy cream. Add garlic powder and season with salt and pepper, to taste, while whisking.
Remove from heat when mixture starts boiling. It should be thick.
Serve potatoes topped with mushroom gravy.