1. Prepare pasta according to package directions.
2. Meanwhile, add potatoes to a medium saucepan. Cover with water and bring to a boil. Boil until soft, about 20 minutes. Drain and mash.
3. Melt butter in a sauté pan over medium heat. Whisk in flour. Slowly add milk and heavy cream and whisk until smooth. Bring to a simmer and cook until sauce thickens.
4. Gradually add mashed sweet potatoes, whisking until smooth. Cook for an additional five minutes.
5. Add pasta, a little bit at a time, to the sauce. Add in cheese and mix until melted. Season with salt. Serve hot.