Preheat oven to 350 degrees F with the rack in the middle position.

Rinse leeks. Slice each in half lengthwise and then into ¼-inch half-rounds. Place in a bowl of cold water and swish them around, separating the layers to remove any grit. Let stand for about 5 minutes, then gently remove the leeks from the bowl with a slotted spoon to a colander. The grit will have fallen to the bottom of the bowl - discard. Rinse the leeks a final time and pat dry.

Heat butter in a 10-inch nonstick, oven-safe skillet until foaming subsides. Add leeks, ½ teaspoon kosher salt, and ¼ teaspoon pepper. Cook until leeks have softened and are just starting to brown, about 5-8 minutes.

While the leeks are cooking, whisk together eggs and heavy cream in a large bowl. Gently stir in salmon, dill, and half of the goat cheese.

Reduce heat to medium and pour the egg mixture over the softened leeks. Use a fork or spatula to evenly distribute the salmon, but don't stir the mixture in the pan. Cook just until the sides of the frittata begin to set, about 2-3 minutes.

Remove from heat and sprinkle the remaining goat cheese over the top of the eggs. Bake for 18-25 minutes, until the frittata has puffed and the center is just set. It should appear soft and custardy in the center, not liquidy (undercooked) or dry (overcooked).**

Let the frittata stand for 5 minutes before cutting into wedges and serving.