Making the most of what you spend on food means making the most of what you have, which often means stretching a dish, kind of like the parable of Jesus, the loaves and the fishes. Restaurants stretch sauces when they need an extra serving or two but not a whole batch -- a technique you can apply in your kitchen with expensive preparations like Alfredo sauce. Alfredo sauce comprises butter, heavy cream and Parmigiano-Reggiano -- all high-end ingredients with no true substitutes. Still, by implementing classic French technique and a few kitchen staples, you can stretch fully cooked Alfredo to twice its quantity at half the cost.
Beurre manie translates as "kneaded butter," and it consists of the same ingredients as roux -- equal parts butter and flour. But beurre manie differs from roux in a couple ways: You incorporate it at the end of cooking, to invest a final flourish of thickening and luster, and you add it cold, or rather at body temperature, as the butter and flour warm as you knead it.
To stretch Alfredo with beurre manie and milk, mix 3 tablespoons each of butter and general-purpose flour by hand. Knead the butter and flour with your fingers and roll it into a ball between your palms until smooth.
In a heavy-bottomed saucepan, bring the Alfredo plus to a low simmer -- it should barely bubble around the edges. Next, stir in 1 cup of whole milk and let it return to a simmer. Pinch off about 1 teaspoon of beurre manie and drop it in the Alfredo, whisking vigorously until it dissolves. Continue adding the beurre manie in teaspoon-sized increments -- wait until the former addition dissolves before adding the next. Simmer the Alfredo for about 10 minutes, or until it thickens to the desired consistency.
Stir in freshly grated Parmesan 1 tablespoon at a time until the Alfredo attains the desired cheesiness, and season it to taste with kosher salt and freshly ground black pepper.
Cornstarch's thickening power is about twice that of beurre manie, but it doesn't impart its buttery finish. However, its cost effectiveness is unrivaled.
To stretch Alfredo with cornstarch, whisk together about 2 tablespoons of cornstarch with 2 tablespoons of cold water until dissolved. Bring the Alfredo sauce to a gentle simmer and stir in 1 cup of whole milk. Let the sauce return to a simmer and slowly whisk in the slurry -- don't empty it in the sauce all at once. Increase the heat until the Alfredo simmers vigorously, whisking constantly, and hold the simmer for 1 minute.
Lower the heat to medium low and continue whisking until the Alfredo stops simmering. Stir in freshly grated Parmesan 1 tablespoon at a time until the sauce reaches the desired flavor, and season it to taste with kosher salt and freshly ground black pepper.
Bechamel, the classic French mother sauce, serves as the foundation of thousands of variants -- cheddar-cheese sauce, sauce soubise and even biscuit gravy are built on this combination of milk thickened with roux. Unlike beurre manie, the flour and butter in bechamel are cooked to a golden color before you add the milk, so you make this Alfredo extender in a separate sauce and whisk it into the finished Alfredo.
For 1 cup of bechamel, melt 1 tablespoon of butter with 1 tablespoon of general-purpose flour in a heavy-bottomed saucepan over low heat. Cook the roux until it attains a blond color and whisk in 1 cup of room-temperature milk. Bring the milk to a simmer, whisking continuously until smooth. Simmer the bechamel for about 10 minutes and add it to the pan of warm Alfredo. Add Parmesan, salt and pepper to taste, and stir until incorporated.
A liaison -- perhaps the most elegant thickener due to the lustrous sheen and velvety mouthfeel it imparts -- is best used when you want to extend the Alfredo by only about 1/2 cup -- it has the least thickening power because it lacks starch.
Add 1/2 cup of whole milk to the Alfredo and stir to incorporate. Heat the Alfredo to about 170 degrees Fahrenheit, or when it barely bubbles around the edges of the pan. Next, whisk 1 egg yolk with 2 tablespoons of heavy cream in a large bowl. Slowly pour about 1 cup of the hot Alfredo sauce into the liaison and whisk vigorously. After combining, pour the liaison and Alfredo mixture back into the Alfredo saucepan and whisk enthusiastically to incorporate. Season the Alfredo with Parmesan, salt and pepper.