Step 1

Preparation Cook shallot in 1 tablespoon butter in a small heavy saucepan over moderately low heat, stirring, until softened. Add wine and boil until liquid is reduced to about 1/4 cup.

Step 2

Reduce heat to low and whisk in remaining 5 tablespoons butter, 1 piece at a time, lifting pan occasionally to cool mixture and adding each piece of butter before previous one has completely melted. Whisk in juice, tarragon, and salt and pepper to taste.

Step 3

Serve beurre blanc in a separate dish with radishes and salt.