Start by separating the eggs. Separate the egg whites into a large bowl and the yolks into another bowl. The best way to do this, in my opinion, is to use clean hands to pass the yolks between and let the whites fall away.
To the egg yolks, add the 25g sugar, milk, melted butter, vanilla extract and salt. Whisk together. Add the plain flour and mix together. Set aside.
With an electric whisk or in the base of a stand mixer in a clean bowl, whisk the egg whites into stiff peaks.
Fold the beaten egg whites into the batter with a large spatula or metal spoon, taking care to not knock out too much air.
Melt a large knob of butter in a large frying pan over medium heat. Once the butter is foaming, pour the batter in the pan and let it gently cook for a few minutes, until the base is set and golden.
Once the base is set, use a spatula to break the pancake into quarters. Flip each quarter to fry the other side. Once the other side is slightly set, use two spatulas to tear the pancake into rough bite-sized pieces, right in the pan.
Once they are small, bite-sized pieces, add the extra 30g butter and 25g sugar (about 1-2 tbsp) to the pan. Toss together so they keep cooking, the edges caramelise and turn crisp and golden.
Transfer the warm Kaiserschmarrn to a serving dish, dust generously with icing sugar and serve straight away, ideally with your favourite topping.