Hi Lisa!
The Danes are famous for their "Smorrebrod"( butter bread) Sandwiches.

Lemon Butter
Cream 1/2 cup softened butter. Gradually stir in 2 tablespoons lemon juice and, if desired, 2 tablespoons finely chopped parsley or dill

Curry Butter
Cream 1/2 cup softened butter. Stir in 1/2 teaspoon curry powder and a little black pepper or a dash of hot pepper sauce.

Mustard Butter
Cream 1/2 cup softened butter. Stir in 1
teaspoon or more prepared mustard, or 1/4 to 1/2 teaspoon dry mustard.

Tomato Mayonnaise
Add 2 teaspoons tomato puree to 1 cup mayonnaise.

Horseradish Mayonnaise
Add a little grated horseradish to taste to mayonnaise.

Note: Both butters and mayonnaise may be flavored in any desired way. Instant onion and garlic powders, dried herbs, bottled sauces, and spices, all lend themselves as flavorings.

From: Classic Scandinavian Cooking (by Nika Hazelton)