Sous Vide: Bechamel (Classic Cream Sauce) with a Simple Application
About
The classic thickened cream is the most commonly used of Escoffier's mother sauces--everything from macaroni and cheese to Lasagne
Ingredients
Classic Bechamel
Cream, 1 cup/240 ml.
Milk, 1 cup/240 ml.
Butter, 2 oz./ 60 g.
Flour, 3 Tablespoons/30 g.
Salt, 2 teaspoons.
White pepper, 0.5 teaspoons
Nutmeg 0.5 teaspoons.
Macaroni and Cheese
Sous Vide Béchamel Sauce, 1 cup/240 ml.
Dry pasta, 5 oz.(by weight)/150 g.
Cheddar cheese, or your preference. 5 oz./150 g.
Salt and white pepper.
Haricot Vert (French green beans), 4 oz/120 g
Egg white, 1 ea.
Flour, 1 cup/128 g.
Baking powder, 1 Tablespoon/12 g.
B2 sauce or your favorite steak sauce...
Equipment requirements
Immersion circulator, portable or stationary.
Heat rated container, minimum of 2 gallons/8 liters.
Heat rated sous vide bags, 2 each.
Flour shaker or fine meshed strainer.
Rubber spatula/wooden spoon.
Kitchen tongs, metal.
Infrared or probe thermometer.
Instructions
Procedure:
In a generic blender, pulse the cream and flour to form a light paste. Add the milk, the butter and the seasonings and pulse again. Do not over mix. Put the mixture in a Ziploc Quart Freezer bag and process in a sous vide bath at 183F/84C for one hour minimum. Remove the bag from the bath and dip it in cold water for one minute--this makes it easier to handle. Carefully transfer it into a 1 qt/1 liter container. It will appear to be separated because there is no friction applied in a sous vide bath.
Using a rubber spatula, stir the sauce in a circular motion (one direction) to incorporate the loose butter. Some cooks finish this sauce with a whip or in a blender, but excessive friction can actually break and thin the sauce. In a few moments, the sauce will look like this: 
The thickness shown may appear overly thick, but this thickness creates the most durable consistency. It is much easier to make this sauce thinner than to make it thicker after it has been finished. 
The sauce should cling to the spatula. 
The chives are added for the purpose of definition! Serve as is, or cool to 70 F/21 C before refrigerating at 40 F/4 C. Here is one of the most popular applications of béchamel--Old Fashioned Macaroni and Cheddar. I garnished with some crispy French cut green beans... 
Procedure:
Cook the pasta as per package directions. Combine with the béchamel and cheese in a Ziploc Freezer Gallon bag. The sauce can be hot or cold, it doesn't matter. Process sous vide at 183/84C for 15 minutes, or until the cheese is melted. Mix in the bag, pour into a heat proof dish or bowl and brown using a torch or the salamander in your oven. Blanch the beans in boiling salted water. Pour the water over the beans and remove from heat. Allow to sit for 5 minutes, drain, and shock to 70F/21C and/or refrigerate at 40 F/4 C--sous vide is not well applied for most green vegetables. Shock cold, drain well, toss in egg white, drain and dredge in the flour/baking powder mixture until dry and loose. Allow to rest, shake off excess flour, and deep fry at 350F/176C until crisp. Garnish with your favorite steak sauce or the B2 linked in the ingredients list!