Preheat the oven to 325°. In a bowl, whisk the eggs with the 1/2 cup of crème fraîche, the tarragon, chopped dill, chives and scallions. Season with 1 1/2 teaspoons of salt and 1/2 teaspoon of pepper.

In a 10-inch ovenproof nonstick skillet, heat 1 tablespoon of the olive oil. Add half of the eggs and cook over moderately low heat, stirring gently, for 5 minutes; keep the heat low enough so the eggs do not begin to scramble. Cook the eggs, undisturbed, for 5 minutes longer. Transfer the skillet to the oven and bake for 10 minutes, or until the eggs are set around the edges and just firm in the center.

Loosen the sides of the frittata with a spatula and gently turn it out onto a wire rack to cool completely. Repeat with the remaining oil and eggs.

Cut the frittatas into 1-inch squares. Garnish with the crème fraîche, salmon and dill sprigs and serve at room temperature.