1. Combine chopped red onion, Skagenröra - or what we English speakers like to call "Swedish prawn mayonnaise" - lemon juice, salt, and black pepper in a bowl. Mix until everything is well incorporated then refrigerate for at least 30 minutes to allow the flavors to meld.

2. Preheat your oven to 350°F or 180°C. Take your rye bread and slice it into triangles, roughly 1 inch or 2.5 cm thick. Toast these until crispy - you want a lovely crunch for the base of your snack.

3. In a separate bowl mix crème fraiche and mayonnaise until smooth, creating a silky and creamy sauce. Add chopped fresh dill, along with a pinch of salt and pepper to taste. This will add a delicate freshness to your dish.

4. To assemble, place a dollop of your shrimp spread onto each toasted rye bread triangle. This is the foundation of your delicious appetizer. Next, top with a slice of smoked salmon - a classic combination with prawn. Add a few pieces of chopped shrimp on top for bite and texture, then sprinkle a bit of fresh dill over everything.

5. Serve immediately - this snack is best enjoyed fresh - and enjoy the delightful combination of flavors and textures!