Step 2: Layer the Ingredients
Place the sliced potatoes in an even layer across the bottom of the prepared baking dish. Sprinkle the diced onion over the potatoes. Break apart the raw ground beef and distribute it in an even layer over the onions, crumbling it into pieces with your fingers as you go — smaller pieces ensure it cooks through evenly and integrates better with the rest of the casserole. Sprinkle the uncooked rice evenly over the ground beef layer. Spoon the drained diced tomatoes evenly over the rice. Sprinkle the chopped celery over the tomatoes if using. The order of layers matters — placing the potatoes on the bottom puts them closest to the heat source so they cook through properly, while the rice in the middle absorbs the liquid that flows down from above.
Step 3: Prepare and Pour the Sauce
In a medium bowl, whisk together the condensed tomato soup, water, Italian seasoning, garlic powder, salt, and pepper until completely combined. The mixture should be smooth, thin, and pourable. Pour this mixture evenly over all the ingredients in the baking dish, tilting the dish slightly if needed to ensure the liquid distributes across the entire surface. The liquid will initially pool on top and will work its way down through the layers during baking — this is how the rice cooks and the potatoes soften.
Step 4: Cover and Bake
Cover the baking dish tightly with aluminum foil. A tight seal is essential — it traps the steam that cooks the rice and keeps the liquid from evaporating before the potatoes have softened. Place the covered dish in the preheated oven and bake for 1 hour and 40 minutes. Resist the urge to lift the foil during cooking, as each peek releases steam and extends the cooking time. The casserole is ready when the potatoes are completely tender when pierced with a knife and the rice has absorbed the surrounding liquid and is fully cooked through. If the potatoes are not yet tender at the 1 hour and 40 minute mark, recover and bake for an additional 15 minutes.
