"This comfort food favorite has been passed down in my family. I remember getting so excited every time my grandfather would make it for us! Although I loved the way my grandfather made it, I've added a few flavorful ingredients of my own. You'll love the bacon, potatoes, sun-dried tomatoes, and bella mushrooms in a potato bake covered with melted Cheddar cheese. Even extra tasty when served with sour cream! This dish is an excellent side dish at dinner or a wonderful addition to a brunch!"
Preheat oven to 350 degrees F (175 degrees C). Butter a 9x13-inch casserole dish.
Heat butter in a skillet over medium heat; cook and stir onions and mushrooms until softened and tender, about 10 minutes.
Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain the bacon slices on paper towels, reserving 1 tablespoon bacon grease. Crumble bacon.
Beat milk, eggs, and reserved 1 tablespoon bacon grease together in a bowl; fold in potatoes until evenly mixed. Stir onion-mushroom mixture and sun-dried tomatoes into potato mixture; season with salt and pepper. Pour potato mixture, including all the liquid, into the prepared casserole dish. Sprinkle bacon and 1 1/2 cup Cheddar cheese over potato mixture.
Bake in the preheated oven until potatoes are tender and cheese is melted, about 55 minutes. Sprinkle remaining 1/2 cup Cheddar cheese over potato mixture and continue baking until melted, about 5 minutes more. Serve with sour cream.