Prep the pan. Heat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with butter. This helps prevent sticking and adds flavor to the edges.

Cube the challah. Cut the bread into 1- to 1.5-inch cubes. If it’s very fresh, spread the cubes on a sheet pan and toast in the oven for 8–10 minutes to dry them slightly.

Make the custard. In a large bowl, whisk together the eggs, milk, cream, granulated sugar, vanilla, cinnamon, nutmeg, and salt until smooth and well combined.

Combine. Add the bread cubes to the bowl and gently toss to coat. Let them sit for 10–15 minutes so the custard absorbs. Fold in any add-ins like raisins or nuts.

Transfer to the dish. Pour everything into the buttered baking dish, spreading it out evenly. Dot the top with small pieces of butter and sprinkle with brown sugar for a caramelized finish.

Bake. Bake for 40–50 minutes, until the top is golden and the center is just set. It should jiggle slightly but not look wet. A knife inserted near the center should come out mostly clean.

Rest and serve. Let it rest for 10 minutes before serving. Spoon into bowls and serve warm, plain or with a drizzle of caramel, maple syrup, or a scoop of vanilla ice cream.