Adjust an oven rack to the middle position and preheat oven to 450 degrees. Coat a 9-inch x 13-inch baking dish with nonstick spray.
On a rimmed baking sheet, spread bread pieces out in a single layer. Toast until crisped and browned, stirring occasionally, about 12 minutes. Cool completely. Reduce oven temperature to 300 degrees.
In a small saucepan over medium-high heat, add raisins and 1/2 cup of bourbon and bring to a simmer (do not boil). Simmer until raisins have softened, about 2 to 3 minutes. Strain the raisins, reserving the liquid.
In a large bowl, whisk together the reserved raisin liquid, remaining 1/4 cup bourbon, heavy cream, milk, brown sugar, egg yolks, vanilla, 1 teaspoon cinnamon, nutmeg, and salt. Add the toasted bread and toss until evenly coated. Let the mixture sit, tossing occasionally until the bread begins to absorb the custard and is softened, about 30 minutes.
Pour half the bread mixture into the prepared baking dish and sprinkle with half of the reserved raisins. Pour the remaining bread mixture into the pan, sprinkle with the remaining raisins and cover with foil. Bake covered for 45 minutes.
Meanwhile, in a small bowl mix the remaining 1/2 teaspoon cinnamon and granulated sugar. Using your fingers, work the butter into the sugar mixture until the size of small peas.
Remove foil from the bread pudding and sprinkle with the cinnamon-butter mixture. Rotate the dish and continue to bake, uncovered, until the custard is just set, about 20 to 25 minutes.
Increase the oven temperature to 450 degrees and bake until the top is crisp and golden, about 10 minutes. Let the bread pudding cool for 30 minutes.