Filling 1: In a bowl, mix the chopped hard-boiled eggs, mayonnaise, mustard, salt, and black pepper.
Filling 2: In another bowl, mix the chopped shrimp, mayonnaise, sour cream, lemon juice, chopped dill, salt, and black pepper.
Filling 3: In a third bowl, mix the chopped ham, cream cheese, mayonnaise, horseradish (if using), salt, and black pepper.
Place one layer of the bread on a serving platter.
Spread Filling 1 (Egg and Mayonnaise) evenly over the bread layer.
Place the second layer of bread on top of Filling 1.
Spread Filling 2 (Seafood) evenly over the second bread layer.
Place the third layer of bread on top of Filling 2.
Spread Filling 3 (Ham and Cheese) evenly over the third bread layer.
Place the final layer of bread on top of Filling 3.
In a bowl, mix the cream cheese, mayonnaise, and sour cream until smooth and well combined.
Spread the frosting evenly over the top and sides of the assembled sandwich cake, covering it completely.
Decorate the smörgåstårta with thinly sliced cucumber, smoked salmon or ham, cherry tomatoes, sliced radishes, fresh dill, fresh parsley, and lemon wedges as desired.
Refrigerate the smörgåstårta for at least 1-2 hours before serving to allow the flavors to meld together.
Enjoy your meal!