Add potatoes to a large pot of lightly-salted cold water. Bring to a boil then cook until potatoes are tender.
Drain, then return empty pot to stove over low heat.
Melt butter in milk then season with salt & pepper.
Add drained potatoes, then mash until smooth.
Turn off heat then place a lid on top of the pot to keep potatoes warm.
Preheat oven to 400 degrees.
Place meatballs onto a non-stick and sprayed baking sheet then bake for about 10 minutes, or until cooked through.
Meanwhile, melt butter in a large skillet over medium heat then sprinkle in flour and whisk until smooth. Cook until mixture is golden brown, about 2 minutes, then slowly pour in beef broth, whisking constantly. Add soy sauce and Worcestershire sauce then switch to a wooden spoon and cook until sauce is thick and bubbly, about 5-7, minutes stirring often. Add frozen vegetables and a generous amount of pepper, then cook until vegetables are tender and heated through, about 3-4 minutes.
Scoop mashed potatoes into serving dish, lining bottom of sides. Top with vegetables with gravy.
Arrange meatballs on top of vegetables and serve.
Shredded cheese can be added before serving.