To make the béchamel, melt the butter in a small saucepan over very low heat. Add the flour and gradually whisk in the milk to avoid lumps. Season with salt, pepper, and nutmeg. Cook, stirring, until the sauce thickens.

Bring a large pot of lightly salted water to a boil. Add the pasta and cook until al dente. Meanwhile, melt the butter in a skillet and add the diced pancetta. Sauté for a few minutes until lightly browned.

Drain the pasta and add it to the skillet with the pancetta. Add a few tablespoons of the pasta cooking water, pour in the homemade béchamel, and mix well.

Sprinkle with grated Parmesan cheese and serve.