Preaheat the oven to 200 degrees Celcius and put an oven safe frying pan it it.
Preheat a nonstick pan over medium heat.
Add a drizzle of olive oil and the minced onion and fry for 1-2 minutes.
Add the asparagus and fry for another 2-3 minutes. The asparagus should just soften a little, but not be cooked through.
Meanwhile combine eggs, milk, sea salt and 1 tablespoon of pesto (optional) in a bowl and whisk using a fork until small bubbles start to appear on the surface.
Take out the pan from the oven using a towel or a potholder, be causeful so you don't burn your hands.
Pour the whisked eggs into the warm frying pan. Add the onions and asparagus, trying to divide it equally around the pan. Place in the oven and bake for 15-20 minutes. The frittata should be golden brown and the eggs should set. But don't bake it for too long, that will make it dryer and not as tasty.
Take out the pan from the oven. Top the frittata with a burrata, about 1 table spoon of pesto and some green leafs. Serve while warm.