Place 5 ounces spinach in a large colander in the sink.
Bring a large saucepan of water to a boil over high heat.
Add 8 ounces spaghetti and cook according to package directions.
Drain the pasta over the spinach; toss to wilt the spinach.
Meanwhile, heat ½ cup sun-dried tomatoes along with 1 tablespoon of the oil in a large skillet over medium heat.
Add ½ cup onion and sun-dried tomatoes; cook, stirring, until softened, about 3 minutes.
Add garlic, ¼ teaspoon crushed red pepper, ¼ teaspoon salt and ¼ teaspoon pepper; cook, stirring, for 1 minute.
Increase heat to medium-high and add 1 cup broth; cook, stirring, until reduced by about half, about 2 minutes.
Stir in ½ cup sour cream, ¼ cup Parmesan and 1 tablespoon butter.
Add the spaghetti and spinach; toss to coat well.
