Adjust broiler rack to 10 inches from heat source and preheat broiler
to high. Beat eggs in a large bowl with 2 generous pinches of salt.
Set aside. In a medium oven-proof non-stick skillet, heat 2 tablespoons
oil over medium-high heat until shimmering. Add onion and cook, stirring,
until just translucent, about 2 minutes. Add diced asparagus and peas,
season with salt and pepper, and cook, stirring, until tender but not
browned, about 6 minutes.
Adjust broiler rack to 10 inches from heat source and preheat broiler
to high. Beat eggs in a large bowl with 2 generous pinches of salt.
Set aside. In a medium oven-proof non-stick skillet, heat 2 tablespoons oil
over medium-high heat until shimmering. Add onion and cook, stirring,
until just translucent, about 2 minutes. Add diced asparagus and peas,
season with salt and pepper, and cook, stirring, until tender but not
browned, about 6 minutes.
Add egg and cook, stirring, until moist curds have formed throughout,
1 to 2 minutes. Transfer skillet to broiler and cook until top is set,
about 3 minutes. Let frittata cool slightly. Run a thin spatula around
and under frittata to detach any spots stuck to skillet.
Invert a large plate over skillet, and in one quick motion turn frittata
out onto plate. Set aside.