As with most sauces originating from Italy, the early Alfredo sauces are not what we Americans are accustomed to. The first recorded recipe dates back to the 16th century, in Rome. A twist on cacio e pepe (starch water, pecorino, and pepper,) the authentic Alfredo is made with a generous portion of butter melted with parmesan.
Where the version made with cream originated is not certain. My guess is that, like with carbonara, some American just added a ton of cream to make it even more unhealthy.
Now, while I'll throw a hissy fit if my carbonara is thickened with cream instead of eggs, I like my Alfredo swimming in thick, velvety cream sauce. I would normally reduce the cream for 40 minutes or so to get the right consistency, but I either grew lazier or smarter, and now use a little flour to speed the process. This sauce really does come together in minutes, so I just dump the pasta in a strainer and make the sauce in the same pot.
FIVE MINUTE ALFREDO SAUCE
12 ounces fettuccini
3/4 cup pecorino cheese, grated, plus more for garnish
2 tablespoons flour
1/4 teaspoon salt
1-1/2 cups heavy cream
Cook the pasta until al dente. Meanwhile, in a small bowl, mix the cheese, flour, salt and pepper. When the pasta is ready, strain. In the same pot used to cook the pasta, add the heavy cream and bring to a simmer. Add the cheese mixture, bring to a boil. Once the sauce has thickened, return the pasta to the pot. Toss to coat with the sauce. Serve immediately.