Bring a large pot of lightly salted water to a boil. Add the rotini pasta and cook for 8 to 10 minutes, or until al dente. Drain and set aside.
In a medium bowl, combine the cream of mushroom soup, melted butter, cheddar cheese, garlic powder, and black pepper. Mix until well combined.
Grease a 2-quart baking dish. Spread the cooked pasta in the bottom of the dish. Sprinkle the cooked bacon over the pasta.
Pour the cream of mushroom mixture over the top of the pasta and bacon.
Bake in the preheated oven for 25 minutes.
Remove from the oven and top with the sour cream. Return to the oven and bake for an additional 5 minutes.
Let cool for 5 minutes before serving. Enjoy!