Preheat your oven to 400°F (200°C). Prepare an ice bath by filling a large bowl with ice and cold water.
Steam the asparagus until tender-crisp, about 5 minutes. Immediately transfer the asparagus to the ice bath to stop the cooking and preserve its bright green color.
Drain well, pat dry, and cut into ½-inch slices. Steam the peas for 5 minutes until tender, then drain.
In a large mixing bowl, whisk the eggs, milk, salt, and pepper until just combined. Be careful not to over-whisk.
Gently stir in the chopped chives, tarragon, prepared asparagus, peas, and the optional Parmesan cheese.
Heat the olive oil or butter in a 10-inch oven-safe skillet (cast iron works perfectly) over medium heat.
Pour the egg mixture into the hot skillet.
Cook on the stovetop, undisturbed, for 5-7 minutes, or until the edges are set and pulling away from the sides of the pan. The center will still be slightly liquid.
Transfer the skillet to the preheated oven.
Bake for 10 to 15 minutes, until the frittata is puffed, golden brown, and the center is fully set.
Remove from the oven and let it rest in the skillet for 5 minutes. Run a spatula around the edge, then slice and serve warm or at room temperature.
Don't over-whisk the eggs.
Whisk just until the yolks and whites are combined. Over-whisking can incorporate too much air, leading to a tough, spongy texture.
