If using raisins, soak them in rum, water or orange juice for about 15 minutes to plump them up, then drain.
Separate the egg yolks from the egg whites. Place the yolks in one bowl and the whites in another.
In a mixing bowl, whisk the egg yolks, milk, flour, sugar, vanilla extract, and salt until smooth and well combined.
Using an electric mixer, beat the egg whites until they form stiff peaks. This will help make the Kaiserschmarrn fluffy.
Gently fold the beaten egg whites into the batter using a spatula. Be careful not to deflate the egg whites; the goal is to keep the batter light and airy.
Heat a 10" large non-stick or cast iron skillet over medium heat. Add half the butter and let it melt, coating the bottom of the pan.
Pour half the batter into the pan, (approximately about ¾” thick layer) spreading it evenly. Sprinkle the drained raisins over the batter if using.
Cook the batter for about 5-7 minutes, or until the bottom is golden brown and the top is mostly set. You can use a spatula to check the underside for colour.
Cut the pancake into quarters using a spatula or two forks and carefully flip each piece over to cook the other side. Alternatively, you can tear the pancake into bite-sized pieces for a more rustic look.
Cook for another 2-3 minutes until the pieces are cooked through and have a nice golden colour.
If you prefer a caramelized version, sprinkle a little extra sugar over the pancake pieces in the pan and let them caramelize slightly.
Once cooked, transfer the Kaiserschmarrn to a serving plate. Dust with powdered sugar and serve with apple or plum compote on the side.
Repeat the same process for the remaining batter.
Kaiserschmarrn is best enjoyed warm, so dig in while it’s hot!