Preheat your oven to 350°F (175°C). Grease the baking dish with butter and set aside.
In a large bowl, combine the cubed bread and diced apples. If using raisins, add them at this point as well.
In another bowl, whisk together the milk, heavy cream, eggs, sugar, vanilla extract, cinnamon, nutmeg, and salt until fully combined.
Pour the mixture over the bread and apple mixture, ensuring all the bread is soaked. Let it sit for about 15 minutes, stirring occasionally to evenly distribute the liquid.
Transfer the bread mixture to the greased baking dish, spreading it out evenly.
Bake in the preheated oven for 45-50 minutes, or until the top is golden brown and a toothpick inserted comes out clean.
Remove from the oven and let it cool for a few minutes before serving.