Preheat the oven to 350 degrees F.
Sauté the onion and asparagus in olive oil in a 10-inch cast iron skillet over medium-low heat until onions are translucent, about 5 minutes.
In a large bowl, beat the eggs.
Add the half and half, feta cheese, smoked salmon, sundried tomatoes, salt, pepper and basil and combine.
Pour the mixture over the onions and asparagus and place the skillet in the center of the oven.
Bake the frittata for about 35-40 minutes, until it puffs up and a knife inserted in the middle comes out clean. Serve warm.