Besciamella Sauce - cooking recipe

Ingredients

5 tablespoons unsalted butter
1/4 cup all-purpose flour
3 cups whole milk
2 teaspoons kosher salt
1/2 teaspoon freshly grated nutmeg

Preparation

Heat butter in a medium saucepan until melted.
Add flour, stirring until smooth.
Cook gently over medium heat until light golden brown, 6-7 minutes.
Meanwhile, heat the milk in a separate pan until almost boiling.
Add milk to the butter mixture 1 cup at a time, whisking continuously until very smooth.
If lumps begin to form, you need to adjust the heat up a bit higher.
Bring to a boil, and cook for 30 seconds, continuing to stir.
Remove from the heat and season with salt and nutmeg.
Note: After I had brought it to a boil and let it cook for 30 seconds, it was still too liquidy.
I continued to cook it over high heat, stirring constantly, until it thickened down, and began to coat the back of the spoon.