Blend to mix thoroughly. Add mayonnaise to bowl. Gradually whisk in mustard mixture until thoroughly blended and smooth. Refrigerate in non-reactive container. Season to taste.
Pluck leaves from mint and basil.
Lay flat in small bundles. Roll bundles individually and mince finely. When finished, chop crosswise to obtain a very fine finished product. Wipe the chives and lemongrass dry. Chop finely in thin slices then crosswise to obtain a very fine finished product.