Prepare the Ground Beef and Aromatics: In a large skillet or frying pan, brown the ground beef over medium-high heat. Use a spoon or spatula to break the beef into crumbles as it cooks. Once the beef is mostly browned, add the chopped yellow onion to the skillet. Continue to cook for another 5-7 minutes, stirring occasionally, until the onion has softened and become translucent. Stir in the minced garlic during the last minute of cooking until it becomes fragrant. Carefully drain off any excess grease from the skillet.

Combine Ingredients in Slow Cooker: Transfer the cooked and drained ground beef and onion mixture into the bottom of a 6-quart or larger slow cooker. Add the frozen diced potatoes, the drained whole kernel corn, and the entire undrained can of Rotel diced tomatoes with green chilies directly into the slow cooker.

Prepare and Add the Creamy Sauce: In a separate medium-sized bowl, whisk together the condensed cream of mushroom soup and the beef broth (or milk) until the mixture is smooth and lump-free. Pour this creamy soup mixture evenly over the ingredients in the slow cooker.

Season the Casserole: Sprinkle the dried paprika, dried parsley flakes (if using), chili powder, garlic powder, black pepper, and about ½ teaspoon of salt over all the ingredients in the slow cooker.

Gently Stir: Using a large spoon or spatula, gently stir all the ingredients together in the slow cooker until everything is well combined and the potatoes are evenly coated with the creamy sauce mixture.

Set and Cook: Place the lid securely on your slow cooker. Cook the casserole on the LOW setting for 6 to 8 hours, or on the HIGH setting for 3 to 4 hours.

Add the Cheese: During the last 30 minutes of cooking time, sprinkle 1 ½ cups of the shredded sharp cheddar cheese evenly over the top surface of the casserole. Replace the lid and continue to cook until the cheese is completely melted and bubbly.

Final Touches and Serve: If desired, just before serving, sprinkle the remaining ½ cup of shredded cheddar cheese, crispy fried onions, or cooked crumbled bacon over the top for an extra layer of flavor and texture.