Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with unsalted butter.

Cut the brioche or challah bread into 1.5-inch cubes and layer half in the prepared dish. Slice tart apples and scatter half over the bread. Repeat with the remaining bread and apples.

Whisk together eggs, whole milk, heavy cream, brown sugar, ground cinnamon, nutmeg, vanilla extract, and a pinch of salt until smooth.

Pour custard mixture over the layered bread and apples, ensure saturation. Cover with plastic wrap and refrigerate for at least 2 hours or overnight.

Bake uncovered for 45-50 minutes, until the top is golden and the center is set. Aroma will signal readiness.

Let cool for 5-10 minutes. Drizzle with warmed caramel sauce and serve warm, optionally with whipped cream or ice cream.