Prepared butter breadcrumbs (melt 1 tablespoons butter in small skillet, stir in breadcrumbs and sauté until golden brown) Cook noodles or macaroni in lightly salted water according to package directions.
Empty sour cream into a large bowl.
Fold in noodles or macaroni.
Melt 3 tablespoons butter in a saucepan.
Stir in flour, salt and pepper; cook until bubbly.
Add soup and tarragon or basil.
Cook, stirring until mixture thickens.
Gradually add sauce to noodles and sour cream, folding continuously.
Fold in pimiento and tuna.
Pour into buttered casserole and sprinkle with buttered breadcrumbs.