To bake the bread pudding: Preheat the oven to 350 F and remove the baking dish from fridge.
Meanwhile, prepare the crumble: Add flour, pecans, dark brown sugar, cinnamon, salt, and butter to a medium bowl, and using your fingertips, rub ingredients together until evenly combined and clumps start to form. Sprinkle the surface of the bread evenly with the crumbs. Bake until the bread pudding is puffy and the top is golden, about 45 minutes to an hour.