Melt butter in a 10-in. ovenproof skillet over medium heat. Add green garlic and cook until it begins to soften, 1 to 2 minutes. Add asparagus and continue sautéing until asparagus is crisp-tender, another 3 to 4 minutes.
Pile nettles into skillet--with tongs!--and toss to wilt and tenderize, 2 to 3 minutes. Season everything with salt and pepper.
Beat eggs with a fork or a whisk in a medium bowl until they are fully blended and just slightly foamy. Season with salt and pepper. Pour eggs into pan over the garlic, asparagus, and nettles, scraping everything out with a rubber spatula.
Let eggs cook without disturbing them for about 1 minute. Then, with a silicone spatula or a table knife, gently lift edges of eggs, letting liquid eggs pour over the edge and underneath. Let that set for another few seconds and then continue lifting and letting eggs flow. This will create layers and make the frittata lighter.
When eggs aren't super runny anymore but top is still moist and undercooked, slide pan under broiler for a minute or two to lightly brown top of frittata.
Careful, the pan handle is hot now! Run spatula or a small knife around edge of frittata and then tip pan over onto a cutting board or cooling rack. Shake and tap to release frittata. If a bit sticks to the pan and rips, don't worry, just piece it back together. Let frittata cool until it's just warm, and serve in wedges.
*Find at farmers' markets and well-stocked grocery stores.