Grease a 9x13-inch baking dish with melted butter and spread the bread cubes evenly.
In a large bowl, whisk together eggs, milk, cream, sugar, vanilla, cinnamon, nutmeg, and salt until smooth.
Pour the custard evenly over the bread and press lightly so the bread absorbs the liquid.
Cover and refrigerate for at least 3 hours or overnight.
Preheat oven to 350°F, remove from fridge, and let stand 20 minutes before baking.
Drizzle melted butter over the top and bake uncovered for 45–50 minutes, until golden and set.
Cool slightly, dust with powdered sugar, and serve warm with syrup and berries.