i *know* this isn't how italians do alfredo, but my family loved this every time i made it before we went dairy free. got it from a co-worker.
1 can evaporated milk (not sweetened condensed, just evaporated)
1 tsp garlic powder (or more to taste)
1/2 tsp salt
1 Tbs cornstarch
1/3 c grated or shredded parmesan cheese
combine first 4 ingredients in a small sauce pan. cook over medium heat until thickened, stirring frequently. add the cheese and cook for another couple minutes. it'll melt and thicken the sauce more.
there ya go. if you try it, i hope you like it!