If using raisins warm up rum or apple juice until just hot. Pour over raisins and let soak for at least 30mins
Separate the eggs into egg yolks and whites and put into two very clean (grease-free) medium sized bowls.
Start by whisking the egg whites with the salt until they are very stiff, using an electric mixer. Set aside.
In the second bowl whisk the egg yolks with the granulated sugar until doubled in size and pale yellow. Slowly add milk while continuing to whisk.
Sift flour into egg yolks and whisk until combined and lump free. Add vanilla powder or vanilla extract.
Peel apple and grate with a box grater (coarse side). Fold apple shreds into egg yolks.
Gently fold 1/3 of the egg whites into the batter. Continue with the other 2 thirds, gently folding from the outside into the middle, making sure you keep as much of the air in the batter as possible.
Immediately place a cast iron or enamel pan over medium heat and melt 1 ½ tablespoon butter until lightly browned.
Gently pour batter into melted butter and turn heat to low.
Bake for 5-6 minutes or until bubbles start rising to the top and the edge of the dough starts to firm up. After 2-3 minutes sprinkle drained raisins, if using, over the dough.
Once the dough as firm up a bit, cut into 4 quarters. Then carefully lift each quarter out of the pan and turn upside down. Continue to cook for another 3-4 minutes, or until the batter has set. With two forks or spatulas rip Kaiserschmarrn into rough pieces.
If you like add another tablespoon granulated sugar and ½ tablespoon butter to the cooked dough and let caramelize quickly over high heat.
Serve with a generous dusting of cinnamon & powdered sugar.
And with apple sauce or stewed fruit, to dip, on the side. (See notes 1 and 2)