Preheat your oven to 375°F (190°C).
In a medium bowl, whisk together the duck eggs, egg whites, sea salt, and black pepper until the mixture is uniform and slightly frothy.
Trim the woody ends off the asparagus and chop the spears into 1-inch pieces.
Heat the olive oil in an 8-inch oven-safe non-stick skillet over medium heat.
Add the minced shallots and chopped asparagus to the skillet, sautéing for 3-4 minutes until the asparagus is bright green and the shallots are translucent.
Pour the egg mixture into the skillet over the vegetables, tilting the pan to ensure the eggs cover the surface evenly.
Allow the frittata to cook undisturbed on the stovetop for 2-3 minutes until the edges are set and pull away slightly from the sides.
Sprinkle the crumbled feta cheese evenly over the top of the eggs.
Transfer the skillet to the preheated oven and bake for 8-10 minutes, or until the center is firm and the top is lightly golden.
Remove from the oven, garnish with freshly chopped chives, and let it rest for 2 minutes before slicing into wedges.