Clean and wash the mushrooms and, depending on size, cut them in half or quarters. Cut ham into strips. Clean and wash spring onions and chives and cut into fine rings.
Whisk eggs and milk. Season with salt and pepper. Stir in chives. Heat oil in a large pan with lid (approx. 28 cm Ø). Fry mushrooms and spring onions in it. Add ham and fry for 1-2 minutes.
Set aside 2-3 tablespoons of the mushroom and ham mixture for sprinkling as desired.
Add the egg milk and spread it evenly in the pan. First let it set slightly on medium heat and push it together from time to time. Then cover and allow to set completely over a low heat for 10-12 minutes.
Cut the frittata into 4 pieces and sprinkle with the remaining mushroom and ham mixture.