01 - Grease a 9x13-inch baking dish and spread the bread cubes evenly within.
02 - In a large bowl, whisk eggs, milk, cream, granulated sugar, brown sugar, vanilla extract, cinnamon, nutmeg, and salt until thoroughly blended.
03 - Pour the custard evenly over the bread cubes, pressing gently to ensure full coverage. Cover and refrigerate for at least 30 minutes or overnight to enhance flavor.
04 - Set the oven to 350°F (175°C).
05 - Mix flour, brown sugar, cinnamon, and salt in a bowl. Cut in cold butter until the mixture forms crumbs. Stir in nuts if using.
06 - Evenly sprinkle the streusel topping over the soaked bread mixture.
07 - Bake uncovered for 40 to 45 minutes until the top is golden and the center is set without jiggle.
08 - Allow to cool for 10 minutes before dusting with powdered sugar and serving alongside warm maple syrup.