If you're using dried shallots, grind them along with the peppercorns in a coffee grinder that you keep specifically for herbs & spices. Do not use a grinder that you use for coffee beans.
If you don't have a grinder, carefully chop the dried shallots to very small bits or bash them with the peppercorns in a mortar & pestle.
If you have fresh tarragon and shallots, chop both and set aside.
Mash a dab of butter with a tablespoon of flour and toast in a small sauce pan.
This is the roux.
When the roux becomes fragrant and nutty,
add the the shallots, pepper, tarragon, lemon juice and zest.
After a smooth paste forms, start adding the milk, a bit at a time, stirring
until it is absorbed.
The consistency is a matter of preference. The sauce should be thick, but
Finish with salt to taste.
Gently spoon over steak & serve with a crisp salad, fingerling potatoes and crunchy French baguette.
Voila! Bon appetit!