Mix eggs, butter, apple syrup, sugar, vanilla extract, cinnamon, nutmeg, cardamom, and salt. together in a large bowl. Stir in half and half and milk. Place cubed bread and currants into a large baking dish. Stir in the egg mixture until bread is evenly coated. Cover and refrigerate for 30 minutes.
Preheat an oven to 350 degrees F (175 degrees C). Uncover the baking dish.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 45 minutes.
