Once butter is melted, sprinkle in flour; whisk until combined
Add milk in ¼ cup increments while constantly whisking; remove from heat
Add the herb(s) of your choice
Add lemon juice and stir well to combine
Season with salt/pepper to taste
Notes
This recipe yields one cup of medium-thin sauce; to make more, keep the same proportions of the ingredients and double or triple the recipe
For a thicker herb cream sauce, add more fat and flour, but don't change the amount of milk
Use unsalted or salted butter and all-purpose flour
Use milk that has sat out of the fridge for about 5 minutes; doesn't have to be room temperature, but you don't want to add cold milk to the butter/flour mixture or the sauce won't work
After the milk is combined, remove the pan from the heat
Add herbs
Stir in acid (use lemon, vinegar or wine) last and OFF HEAT
If you use fresh herbs, use 3X as much; dried herbs are stronger than fresh
Season with ½ teaspoon of salt at first; add more if you like
Serve immediately; sauce will thicken upon standing
If you make it in advance, reheat on the stovetop on low heat and plan on adding a little more milk until it reaches the consistency you want