Danish Shrimp Sandwich (Reje Mad)

Several slices of dark rye, thinly sliced
Unsalted butter
1 head Boston or butter lettuce
Good-quality mayonnaise (about 2 tablespoons)
6 to 8 large cooked shrimp
Thinly sliced lemon
Watercress or dill for garnish

Butter several slices of bread, cutting in half if slices are very large.
Top each with leaf lettuce so that it extends over sides of bread.
Top lettuce with generous lump of mayonnaise, about 1 teaspoon.

Place 2 large shrimp beside each other on top of mayonnaise, so mayonnaise holds them in place.
Put another dab of mayonnaise on top, followed by thin twist of lemon and sprig of watercress or dill for color.