French Toast Casserole

Name: French Toast Casserole
Ingredients: 1 1-lb. challah, brioche, or Pullman loaf, sliced 1 thick; 3 Tbsp. unsalted butter, melted, plus more for pan; 6 large eggs; 1¾ cups heavy cream; 1¾ cups whole milk; ⅓ cup (packed) light brown sugar; 1½ tsp. ground cinnamon; ½ tsp. ground cardamom; ¾ tsp. kosher salt; ½ tsp. finely grated orange zest (optional); 1 Tbsp. demerara sugar; ½ cup crème fraîche; Maple syrup (for serving)