Asparagus Frittata with Horseradish Sour Cream

Heat the oven to 400°F and arrange a rack in the middle.

Heat the oil in a large oven-safe nonstick frying pan over medium heat until shimmering.

Add the onion, season with salt and pepper, and cook, stirring occasionally, until softened and lightly browned, about 5 minutes.

Add the asparagus, season with salt and pepper, and cook, stirring occasionally, until the asparagus is crisp-tender, about 5 to 6 minutes more.Meanwhile whisk the eggs, milk, cheese, horseradish, parsley, measured salt and pepper, and nutmeg in a large bowl until evenly combined.Turn off the heat, pour the egg mixture into the pan with the asparagus mixture, stir with a rubber spatula to combine, and spread the asparagus into an even layer.

Transfer the pan to the oven and bake until the frittata is puffed and just set in the center, about 10 to 12 minutes.

Remove the pan to a wire rack and let it cool slightly, about 5 minutes.Loosen the edges of the frittata with a rubber spatula and slide it onto a cutting board. Slice it into wedges and serve immediately, passing the horseradish sour cream and chives on the side.