Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan with butter or cooking spray, then line with parchment paper, leaving overhanging edges for easy removal. If your bread isn't already stale, spread the cubes on a baking sheet and toast in the oven for 10 minutes until slightly dried out but not browned.
In a medium saucepan, melt the butter over medium heat. Add the diced apples, brown sugar, cinnamon, nutmeg, and lemon juice. Cook for 7-8 minutes, stirring occasionally, until the apples are softened but still hold their shape. Allow the mixture to cool for 5 minutes.
In a large bowl, whisk together eggs, milk, heavy cream, granulated sugar, vanilla extract, cinnamon, nutmeg, and salt until well combined. The mixture should be smooth and slightly frothy.
Add the bread cubes to the custard mixture, gently folding until all pieces are evenly coated. Let stand for 15 minutes, stirring occasionally to ensure even absorption.
Layer half of the soaked bread mixture into the prepared loaf pan. Spoon two-thirds of the apple mixture evenly over the bread layer, pressing gently. Top with the remaining bread mixture and finish with the remaining apple mixture. Press down lightly to compact the loaf.
Cover the loaf pan with aluminum foil and bake for 30 minutes. Remove the foil and bake for an additional 25-30 minutes until the center is set and the top is golden brown. A knife inserted in the center should come out mostly clean with just a few moist crumbs.
Allow the loaf to cool in the pan for 15 minutes, then use the parchment overhang to lift it out and transfer to a wire rack. If using the glaze, whisk together the powdered sugar, apple cider or milk, and vanilla until smooth. Drizzle over the warm (not hot) loaf.