I've been working with a Danish cookbook, and I can tell you that Danish food is all about dairy products and seafood. Delicious and undeservedly overlooked. I think Danes consider smorrebrod the national dish of Denmark.
Whip the cream until it holds soft peaks. Whisk in sour cream, horseradish and salt and pepper to taste.
Pit and slice the avocadoes and drizzle with lemon juice.
Spread the butter evenly on each slice of bread, going all the way to the edges. (Butter prevents the filling from making the bread soggy.) Arrange shrimp, avocado and onion over the bread, then top with a spoonful of horseradish sauce. Add a few capers.