Heat a skillet over medium-high heat (about 375°F) for 2 minutes until hot. Add 1.5 pounds of ground beef and break it apart with a wooden spoon. Cook for 6 to 8 minutes until the meat is fully browned and no pink remains. Listen for a steady sizzle as the moisture cooks off and the meat browns evenly. Drain any excess grease from the skillet so your CrockPot Beefy Potato Taco Casserole doesn't turn greasy during the long simmer. Stir in 1 packet of taco seasoning and 1/4 cup of water. Simmer for 2 minutes until the sauce coats the beef. (I skipped browning the beef once, the excess grease made the potatoes soggy so don't skip this step.) Cook at medium-high not low heat, high heat browns the beef fast so it stays juicy.

Lightly grease the inside of a 6-quart slow cooker insert with cooking spray. Place 4 cups of cubed Russet potatoes in an even layer at the bottom of the pot. Spread the cooked seasoned ground beef directly over the potatoes. You'll see the pale white potato cubes nestled tightly under the dark seasoned beef layer. Pour 1 can of diced fire-roasted tomatoes with their juices over the meat to provide cooking liquid. Do not stir the layers together yet. Keeping the potatoes on the bottom ensures they sit directly against the heat element and cook until tender. Layering bottom-to-top, bottom potatoes catch the heat while top juices drip down to soften them.

Place the lid securely on the slow cooker. Set the power to LOW heat and cook for 5 to 6 hours or HIGH heat for 3 to 4 hours. Avoid lifting the lid during the first 3 hours of cooking. When done, you'll smell rich taco spices filling the kitchen and the potatoes will yield easily when pierced with a fork. The tomato juices will have thickened into a savory sauce surrounding the tender potatoes. If you remove the lid early you lose valuable steam and add 20 minutes to cook time. (My first test batch on HIGH for 2 hours left the potato centers crunchy, give them the full 3.5 hours minimum.) Cook on LOW heat, gentle heat softens starch without breaking potato cubes down into mush.

Scatter 2 cups of shredded sharp cheddar cheese evenly across the hot casserole surface. Cover with the lid and cook on LOW for 10 to 15 minutes until the cheese is completely melted and bubbling. The surface will turn into a glossy layer of bright golden melted cheese with red tomato specks poking through. Turn off heat and sprinkle with 1/4 cup of sliced green onions and fresh cilantro. Rest for 10 minutes uncovered before serving to allow the casserole structure to set up slightly. Rest 10 minutes off heat, lets steam escape so the cheese layers cling cleanly to each serving spoon.