Preheat your oven to 375°F (190°C) and grease a 9x13 inch baking dish to prevent sticking.

In a large pot of salted boiling water, cook the rotini until just al dente, about 8-10 minutes. Drain the pasta and set aside.

Heat a tablespoon of olive oil in a large skillet over medium heat. Add diced onions and sauté until translucent, about 3-4 minutes.

Stir in the ground beef, breaking it apart with a spatula. Cook for about 5-7 minutes, until browned.

Add minced garlic, stirring for about a minute until fragrant.

Toss in the sweet corn and ranch seasoning mix, stirring for another 2 minutes.

In a separate bowl, whisk together the sour cream, shredded cheddar cheese, and milk until smooth.

In a large mixing bowl, combine the cooked rotini with the beef mixture and pour the cheese sauce over. Stir gently until evenly coated.

Add salt and pepper to taste, then transfer to the greased baking dish.

Bake for 25-30 minutes, or until the top is bubbling and golden brown.

Let cool for about 5 minutes before serving. Garnish with fresh parsley.