If your shrimps are uncooked and unpeeled,proceed to cook them and peel them. I have used cooked han-peeled shrimps in brine, so mine came lightly salted and ready to use.
Combine the mayonnaise, creme fraiche, lemon juice, sriracha, 3 tablespoon chopped dill and a pinch of salt in a bowl. Stir in the fish roe. Add this mixture to your shrimps and mix to combine.
Set a skillet on medium heat and melt half of the butter. Place the bread slices in the skillet and toast them on both sides for 2-3 minutes. Increase heat if necessary. Use remaining butter before adding the rest of the slices.
Let the toasted bread cool for a couple of minutes, then top with shrimp salad. Decorate with extra dill and a small lemon slice.
Notes
If making this in advance, let the bread rest on a cooling rack and top the sandwiches just before serving to prevent the bread from going soggy.