If you don't like cooking with alcohol, use the white vinegar and two tablespoons of white grape Juice instead.

1. Simmer and reduce the liquids, with garlic, shallots, and bay leaf:
Place first six ingredients (clam juice, sherry, whole milk, garlic, shallots, bay leaf) in a small saucepan. Heat on medium high heat and let simmer until the liquids have reduced by about half.

2. Make a roux: In a separate saucepan prepare the roux. Heat one tablespoon of butter in the saucepan on medium heat until it is foamy. Sprinkle in the flour, stirring a couple of minutes with a metal whisk until well mixed (tan, but not browned).

3. Add liquid mixture to roux:
Slowly add the reduced mixture to the roux, stirring quickly to incorporate. When you first add some of the mixture, the roux will bubble up. Just keep adding the mixture and keep whisking to incorporate.

4. Slowly incorporate butter:
Lower the heat to low. Remove the bay leaf. Slowly whisk in the butter. Let the butter fully melt and be incorporated into the sauce.

5. Stir in lemon juice, salt, and white pepper. Add some more clam or chicken stock or water if the sauce is too thick.

TIPS:
You can use a half & half instead of milk and add small shrimp & crabmeat plus an extra squeeze of fresh lemon juice for an excellent variation.
You also can reduce butter to 1 stick and add canned fire roasted tomatoes for another lovely variation.