Soak the raisins in rum overnight. This step is optional, you can use non-soaked raisins in žemlovka if you want, nothing will happen.
Preheat the oven to 340 °F (170 °C)
Begin with preparing the baking pan. Grease it with one tablespoon of butter, set it aside.
Make the egg custard: Pour lukewarm milk into a large bowl, add melted butter, granulated sugar, and whole eggs. Whisk until combined. I used a handheld mixer on very low speed.
Slice the stale bread into pieces about ½ inch thick.
Peel and core the apples, slice them thinly.
Soak the pieces of sliced bread in the egg custard. Then, lay them down into a baking pan as the lowest layer.
Cover the bread layer with sliced apples. Sprinkle apples with granulated sugar, cinnamon, and raisins.
For the top layer, soak the rest of the white bread in the egg custard and place them over apples. If you have any egg custard left, drizzle it on the top of the žemlovka.
Bake for 40 minutes until the surface is golden and crispy.
Allow the žemlovka to rest for 10-15 minutes before serving. Serve warm, sprinkled with powdered sugar.