Make the Streusel:
In a large bowl, stir together the flour, almonds, brown sugar, granulated sugar, cinnamon, and salt. Stir in the butter and then use your fingertips to blend the streusel until it forms uneven clumps. Set aside.
Make the Bread Pudding:
Preheat the oven to CONVECTION/BAKE 350°F. Grease a 9-by-13-inch baking dish with the softened butter. Place the bread chunks in the baking dish in an even layer and set aside.
Whisk together the milk, cream, eggs, maple syrup, brown sugar, vanilla extract, cinnamon, allspice, salt, nutmeg, and almond extract (if using) in a large bowl, then pour it over the bread. Gently press the challah down until submerged, then let the mixture stand for about 10 minutes. Sprinkle the streusel evenly over the top. Bake until puffed and golden brown, about 40 minutes. Remove from the oven and set aside for 10 minutes before serving.
Make the Buttered Maple Syrup:
While the bread pudding cools, combine the maple syrup, butter, brown sugar, and salt in a 2-cup heat-safe measuring cup. Microwave on high for 15-second intervals, stirring in between, until the butter is melted. Serve the bread pudding with the buttered maple syrup.
Omit the streusel. Omit the nutmeg and almond extract. Just before baking, sprinkle 2 cups fresh raspberries over the top of the bread pudding, pressing some of them into the custard. Sprinkle 3⁄4 cup coarse raw sugar (such as turbinado) over the berries before baking. Increase the baking time to 50 minutes. For the syrup, substitute 1 cup seedless raspberry jam for the maple syrup and omit the brown sugar.
Omit the streusel. Increase the vanilla extract to 4 teaspoons and omit the cinnamon, allspice, and nutmeg. Substitute 1 tablespoon finely grated orange zest and 1⁄4 teaspoon orange oil for the almond extract. Sprinkle 3⁄4 cup coarse raw sugar (such as turbinado) over the top before baking.
Like most bread puddings, you can also assemble this one the night before, then just sprinkle it with streusel before baking.
For the best results when baking, be sure the rack is in the middle position. If you’re working with a tall pan, such as a Bundt pan, use the bottom position.