2 T. butter
2 T. flour
3/4 tsp. salt
1/4 tsp. dry mustard
1 c. milk
2 egg yolks
grated rind of 1 lemon
1 T. lemon juice
1 T. capers, drained
1/4 c. chopped flat leaf parsley
1 tsp. dried dill or 2 tsp. fresh dill
1 c. sour cream

Melt butter in a small saucepan over low heat. Blend in flour, salt and dry mustard. Cook for 1 minute. Slowly add milk, whisking constantly, until thickened and smooth. Combine egg yolks with lemon rind, juice, capers, parsley and dill. Add 2 tablespoons of hot milk mixture to the eggs and stir together. Return entire egg mixture to milk mixture in saucepan. Stirring constantly, bring to a gentle boil. Remove from heat and stir in sour cream. Keep sauce warm over a double boiler. This is also good with steamed asparagus.