In a large skillet over medium heat, cook 1½ pounds ground beef until browned. Drain excess fat but leave a thin layer for flavor.
Add 1 diced onion and cook until softened, about 4–5 minutes. Stir in 3 cloves minced garlic and cook 30 seconds.
Add 8 ounces chopped mushrooms and cook until moisture evaporates and mushrooms begin to brown.
Reduce heat to medium-low. Stir in 2 tablespoons butter and allow to melt. Sprinkle in 2 tablespoons flour and cook, stirring, for 1–2 minutes to form a roux.
Gradually whisk in 1½ cups milk and ½ cup beef broth, stirring constantly until thickened.
Add 1 tablespoon Worcestershire sauce, 1 teaspoon kosher salt, and ½ teaspoon black pepper. Simmer until mixture is creamy but not loose.
Fold in 1½ cups frozen mixed vegetables and 1 cup shredded cheddar (if using).
Transfer mixture to a 9x13 baking dish, spreading evenly.
Arrange frozen tater tots in tight rows over the top, covering completely. Do not thaw.
Bake uncovered for 40–45 minutes, until the base is bubbling and the tots are deeply golden and crisp.
Let rest 10–15 minutes before serving to allow the structure to set.
Notes
NotesThe base should be creamy but thick before baking. If it looks soupy, simmer longer before transferring.For extra crispness, lightly brush tots with melted butter before baking.For nostalgic version, substitute 1 can condensed cream of mushroom soup for the scratch sauce and reduce milk to ½ cup.StorageRefrigerate covered up to 4 days.Reheat uncovered at 325°F until warmed through to preserve crisp topping.Freeze baked and cooled hotdish tightly wrapped up to 2 months.This is structurally sound and Midwest-authentic — not shepherd’s pie cosplay.Next move in the cluster: Chicken & Wild Rice Soup or Tuna Noodle Casserole?