The Best Baked Ziti Ever

Why I Love This Recipe
This ziti is a favorite with our friends and family. And we actually have friends that we visit up in New Hampshire who joke that we're not allowed into their house unless we bring a pan of this ziti, so we always do!
This is a great make-ahead meal. Prepare it, put it in the fridge and then bake it a day or two later. Just remember that it will take longer to heat through if it's been in the fridge, so you'll need to leave it in the oven for an extra 20 minutes or so.
Ingredients You'll Need
1 pound dry ziti pasta
1 onion, chopped
1 pound lean ground beef
2 (26 ounce) jars of your favorite pasta sauce
6 ounces provolone cheese, sliced
16 oz. container sour cream
10 ounces mozzarella cheese, shredded
2 tablespoons grated Parmesan cheese
1 package sliced pepperoni (optional)
Directions
Bring a large pot of lightly salted water to a boil. Add ziti pasta, and cook until al dente, about 8 minutes; drain.
In a large skillet, brown onion and ground beef over medium heat. Add spaghetti sauce, and simmer 15 minutes.
Preheat the oven to 350 degrees F (175 degrees C). Butter a 9x13 inch baking dish. Layer as follows: 1/2 of the ziti, pepperoni, Provolone cheese, sour cream, 1/2 sauce mixture, remaining ziti, mozzarella cheese and remaining sauce mixture. Top with grated Parmesan cheese.
Bake for 30 minutes in the preheated oven, or until cheeses are melted.