Heat the milk in a large saucepan over medium-low heat to 185 degrees F.
In a separate large pot over medium heat, make the roux by melting the butter and slowly whisking in the flour and onion powder. Once the milk has reached temperature, add the roux and the cheese. Using an immersion blender, carefully blend all ingredients until smooth. Season with salt and pepper. Stir in the macaroni.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Sisters and Brothers, Seattle, WA