Put the potatoes in a saucepan and cover with water by 1 inch; season with salt. Bring to a boil and the simmer for about 20 minutes. Drain and return to saucepan. Set aside. Preheat the broiler. In a medium bowl, combine meats, breadcrumbs, egg, 1/2C broth, 1/2 tsp salt and some pepper. With hands, mix til combined and then form 2" meatballs and arrange on a rimmed baking sheet. Broil for 7 minutes.

Melt 1 Tbsp butter in a large pot over high heat. Add the mushrooms, 1/2 tsp salt and some pepper. Cook, stirring constantly for about 8 minutes. Sprinkle in the flour and stir to coat. Stir in the wine and bring to a boil. Add 1C broth and return to a boil, then reduce heat to medium high and add the meatballs. Simmer, stirring occasionally while you mash the potatoes.

Add 5 Tbsp butter and 1/2C broth to the potatoes to mash. Season with S&P. Stir in parsley to the meatball sauce mixture and serve over the potatoes.