Recipe found on Martha Stewart’s website

3 TB unsalted Butter

1/2 cup minced Onion

1/3 cup All-purpose Flour

4 cups Whole Milk, room temperature

Coarse Salt and freshly ground black Pepper

About 1 3/4 lb Spinach, trimmed, washed and cut crosswise into 1/2” thick strips

5 oz Gruyere Cheese, grated 2 cups

3/4 lb Elbow Macaroni, cooked according to package instructions

In a large saucepan, melt butter over medium.  Add onion and cook until translucent, 6 minutes.  Whisk in flour and cook, stirring frequently, until mixture is pale golden and has a slightly nutty aroma, about 2 minutes.  Whisking constantly, add 2 cups milk.  Add remaining 2 cups milk, raise heat to medium-high, and whisk until smooth; season with salt and pepper.  Cook, whisking constantly until sauce comes to a boil, 8 to 10 minutes.  reduce heat to low and simmer gently, stirring occasionally, until sauce thickens, 13 to 15 minutes.  Add spin each and cook, stirring constantly, until wilted, about 3 minutes.  Add cheese and stir until melted, about 2 minutes.  Add cooked macaroni and stir to combine.  Serve immediately.