1 pound asparagus, tough ends snapped off, cut on the bias into 2 1/2-inch pieces
1/4 cup chopped fresh dill, plus more for garnish
Place an oven rack in the upper third of the oven and preheat oven to 375 degrees.
Add the eggs, cashews, lemon juice and salt to a high speed blender, and process until smooth and creamy. Set egg mixture aside.
Heat 2 tablespoons of the oil over medium-heat in a 9 or 10-inch oven-proof skillet. Add the leeks and onions and 1 tablespoon of water; cook, stirring occasionally, until the leeks are wilted and tender, about 3-minutes. Add the asparagus and cook for 1 minute. Remove the vegetables to a mixing bowl. Wipe out the skillet and let it cool until tepid.
Gently stir the cooked vegetables into the egg mixture. Fold in the dill.
Heat the remaining tablespoon of oil in the skillet over medium heat. Pour in the egg and vegetable mixture. Cook until the eggs just begin to set on the bottom. Using a heat-resistant spatula, gently lift the edges of the cooked eggs and let liquid eggs run under to the pan below. Cook for another minute and repeat. When the bottom half of the eggs are cooked, place the pan in the oven and cook for about 5 minutes, until the eggs are no longer wobbly at the center. Turn on the broiler and broil the frittata until lightly browned on the top, about 30 seconds.
Remove the frittata from the oven and let sit at least 5 minutes in the pan, then slice and serve.