Bring a small pot of water to a boil. Meanwhile, peel the sweet potato and cut it into 1/2-inch pieces. Add the sweet potato to the boiling water and cook until very tender, about 10-20 minutes. Drain well.
1 medium sweet potato
For a completely smooth sauce, puree the cooked sweet potato with an immersion blender, small food processor or high-speed blender until smooth. For a more textured sauce, mash it very well until no lumps remain. Measure out 1 cup (245 grams) and set aside.
Bring a medium pot of generously salted water to a boil. Add the macaroni and cook until al dente. Drain and set aside.
3 cups elbow macaroni
While the pasta is cooking, heat the olive oil in a large saucepan over medium-high heat. Add the flour and whisk constantly for 1 minute.
2 tablespoons olive oil or butter, 2 tablespoons all-purpose flour or for a gluten-free version, use Bob's Red Mill 1-to-1 Gluten-free Baking Flour
Slowly pour in the milk while whisking constantly. Cook, whisking frequently, until the sauce is thick enough to coat the back of a spoon, about 3-5 minutes.
2 cups whole milk
Reduce the heat to low. Stir in the Dijon mustard, if using, garlic powder, cheese and 1 cup (245 grams) of the pureed or mashed sweet potato. Cook for another few minutes, if needed, until the sauce is thick and smooth.
1/2 teaspoon Dijon mustard, 1/2 teaspoon garlic powder, 2 cups freshly grated cheddar or a mix of cheese
Add the salt, pepper and drained macaroni. Stir until the macaroni is evenly coated with the sauce. Taste and adjust the salt and pepper if needed. Serve hot.
1/2 teaspoon salt, 1/4 teaspoon freshly ground black pepper