- Put the milk in a small saucepan to heat up. In a separate saucepan, melt the butter and as it just begins to foam, remove it from the heat and add the flour, stirring until it becomes a smooth paste. Then add a splash of the warm milk and stir until smooth.
- Return the pan to a very low heat and slowly pour in the rest of the milk, stirring all the time , until all combined. If your sauce is smooth now, it will most likely remain smooth. So you want to make sure you have no lumps if possible. Season with the salt and a little white pepper.
- Now the sauce needs to be cooked for at least 10 minutes to ensure the flour taste is cooked out. You must stir it all the time on a very low heat. My cooker does not have a gas ring low enough to do this as slowly as it needs so I transferred my sauce to a bain marie after 6 minutes.
- After 5-10 minutes of cooking, depending on the heat cooked at, place your pan in another larger pan of simmering water (bain marie) to continue cooking gently for another 5 minutes, stirring continuously.
- Meanwhile, in a frying pan, melt the butter and fry the asparagus chunks for 3 minutes. Then add your scallops and fry for just 2 minutes on each side.
- Once the sauce is ready, pour your asparagus and scallops into the sauce and stir to coat. Transfer to 2 shallow oven dishes and cover with a sprinkle of Gruyere cheese. Place under a medium grill for 5 minutes or until the cheese is golden and bubbling.
Sauce from French Provincial Cooking by Elizabeth David