Prep the slow cooker: Grease the inside of a 5- or 6-quart crockpot with butter or nonstick spray.
For easier cleanup, you can line it with parchment that comes up the sides.
Cube the bread: Cut into 1-inch pieces. If the bread is very fresh, spread cubes on a sheet pan and let them sit out for 30–60 minutes to dry slightly. This helps them soak up the custard.
Whisk the custard: In a large bowl, whisk eggs, milk, cream, sugar, vanilla, cinnamon, nutmeg, and salt until smooth and no streaks of egg remain.
Combine: Add bread cubes and any dried fruit to the bowl.
Toss gently to coat every piece. Let the mixture sit for 10–15 minutes so the bread absorbs the custard.
Transfer to the crockpot: Pour the mixture into the greased crock, spreading it evenly. Drizzle the melted butter over the top and sprinkle with brown sugar.
Cook low and slow: Cover and cook on Low for 3 to 4 hours, or until the center is set and the edges are slightly puffed.
A knife inserted in the middle should come out mostly clean with a few moist crumbs.
Optional finish: If your slow cooker insert is oven-safe, you can place it under the broiler for 2–3 minutes to caramelize the top. Watch closely to avoid burning.
Rest and serve: Let it rest for 10 minutes to firm up. Serve warm with vanilla ice cream, whipped cream, a drizzle of caramel sauce, or a splash of warm cream.