2) In a large pot of boiling salted water, add rotini and cook for 6-8 minutes until tender. Drain and set aside.
3) In a saucepan over medium-high heat, melt half of the butter and add the onions. Add the flour and pepper and mix until mixture is pasty and forms a roux. Whisk milk into pan, incorporating the roux. Bring to a simmer over low heat and allow to thicken; about 5 minutes. Once thickened, whisk in the cheeses. Add the pasta and mix until the pasta is well coated. Fold in spinach, sun-dried tomato oil and sun-dried tomatoes.
4) In a small saucepan, melt remaining butter over medium heat. Once melted, turn heat off and add breadcrumbs and paprika. Mix well to combine.
5) Pour rotini into a casserole dish large enough to hold the pasta. Sprinkle the top with breadcrumbs and place in oven for 15-18 minutes or until brown and bubbling.