Step 1: Brown the Ground Beef - Start by heating a large skillet over medium high heat. Add the ground beef along with the salt, pepper, and garlic powder. As the beef cooks, break it apart with a spoon until you have nice crumbles and no pink remains. This step builds the flavor foundation for the whole casserole, so do not rush it. Once the beef is cooked through, carefully drain off any excess grease so the casserole stays rich but not greasy.
Step 2: Season the Beef Mixture - Sprinkle the taco seasoning over the cooked beef and pour in the water. Stir everything together well and let it simmer for a couple minutes until the mixture thickens slightly. The smell at this point is incredible and usually brings everybody into the kitchen asking what is cooking. Stir in the drained Rotel tomatoes and sour cream until everything is creamy and evenly combined.
Step 3: Prep the Slow Cooker - Lightly grease the inside of your slow cooker to help prevent sticking. I usually use a little cooking spray or rub a bit of oil around the sides. This simple step makes cleanup much easier later on which is always a win in my book.
Step 4: Layer the Potatoes - Add a layer of thin sliced potatoes to the bottom of the slow cooker. Try to overlap them slightly so you create an even base layer. Thin slices are important because they cook more evenly and become perfectly tender by dinnertime.
Step 5: Add the Taco Beef - Spoon part of the taco beef mixture over the potatoes and spread it out evenly. You want every bite to get some of that creamy taco flavor. After the beef layer, sprinkle a generous layer of shredded cheddar cheese over the top.
Step 6: Repeat the Layers - Continue layering potatoes, taco beef mixture, and cheese until everything is used up. Finish with cheese on top because that golden melted layer is half the reason everybody comes back for seconds. Once assembled, place the lid on the slow cooker.
Step 7: Cook Until Tender - Cook the casserole on low for about 5 to 6 hours or on high for 3 to 4 hours. The potatoes should be fork tender and the cheese should be melted beautifully throughout the casserole. Every slow cooker runs a little differently, so check the potatoes near the end of cooking time.
Step 8: Let It Rest Before Serving - Once cooking is finished, let the casserole sit for about 10 minutes before serving. This gives the layers time to settle and makes scooping much easier. Trust me, it is worth the short wait. The casserole holds together better and tastes even richer after resting a few minutes.