Assemble smoked-salmon tea sandwiches with herb butter on grain bread a day in advance, and cut before guests arrive.
In a bowl, combine the butter, chives, dill, lemon juice, salt, and pepper.
Lay out the bread slices; spread with prepared butter mixture. Top half the slices with the smoked salmon. Lay remaining slices, buttered-side down, on top of the salmon. Place sandwiches on a baking sheet, cover with plastic, and place in refrigerator until the butter is cold, about 30 minutes.
Transfer sandwiches to a cutting board. Trim crusts from sandwiches, and cut in half to form thin rectangles. Serve chilled.