Preheat the oven to 400 degrees . In a 10-inch, ovenproof nonstick skillet, heat 2 tablespoons butter over medium heat. Add 3 thinly sliced leeks and cook, stirring frequently, until softened, about 5 minutes; season with salt. Stir in 1 bunch asparagus, halved lengthwise and cut into 1-inch pieces; cover and cook until crisp-tender, 3 to 5 minutes. In a large bowl, whisk 10 eggs with 1/2 teaspoon salt and 1/4 teaspoon pepper. Stir in 5 ounces crumbled soft goat cheese. Pour over the vegetables in the skillet, arranging the asparagus and leeks evenly. Bake in the oven until the eggs are set, about 15 minutes. Meanwhile, in a small bowl, combine 1/3 cup sour cream, 2 ounces goat cheese and 3 tablespoons chopped fresh chives; season with salt and pepper. Run a spatula around the inside edge of the skillet and slide the frittata onto a cutting board. Slice into 6 wedges. Transfer to plates and serve with a dollop of the herbed goat cheese mixture and more chopped chives.