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