Halve the eggs lengthwise and separate the yolks from the whites. Place the softened butter in a large enough bowl. Push the egg yolks through a kitchen sieve and mix them into the butter. Season the egg yolk mixture with mustard, salt and freshly ground pepper to taste.
Toast the bread and spread it thickly with the egg yolk mixture. Chop the egg white and spread evenly on the toast together with fine lettuce strips and the Greenland shrimp. Fold two slices of toast into a sandwich and cut crosswise.
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