Steam eggs in a vegetable steamer 16 minutes; cool slightly, and peel. Slice eggs in half lengthwise, and remove yolks; mash yolks.
Sauté panko in butter for 2 minutes. Stir mayonnaise, sour cream, green onions, parsley, tarragon, Dijon mustard, lemon juice, salt, and pepper into yolks. Divide among whites; top with panko.