Arrange the brioche or challah cubes in a greased 9x13 dish in an even layer, so the top looks mostly covered. Press any tall pieces down slightly to help them soak uniformly.

Whisk the eggs, whole milk, heavy cream, pumpkin puree, maple syrup, brown sugar, pumpkin pie spice, cinnamon, vanilla, and salt until smooth, with no streaks of pumpkin or spices visible. Pause and whisk 20 seconds longer if the mixture looks speckled.

Pour the custard over the bread and press down gently until most cubes are submerged. Cover and refrigerate overnight (chilling) so the bread absorbs the liquid.

Preheat the oven to 350F and keep the chilled casserole covered until you’re ready to top it. Let it sit 10 minutes while the oven heats if it feels very stiff.

Make the streusel by rubbing flour, brown sugar, cinnamon, and cold butter together until the mixture looks like coarse crumbs. Leave some pea-size bits so the topping stays crisp when baked.

Scatter the streusel over the soaked bread in an even layer, covering most of the surface. Don’t press it down—leave it loose for a puffed, crunchy top.

Bake for 50-55 minutes at 350F until the casserole is golden and puffed in the center. The edges should look set and the middle should no longer look wet.

Let the casserole rest 5 minutes after baking so the custard firms up slightly. Serve warm with warm maple syrup and powdered sugar for a sweet finish.