How to Make It
Preheat the oven to 350°. In a small bowl, cover the prunes with the pisco and let stand for 1 hour, until plump. Meanwhile, bring a medium saucepan of water to a boil. Add the kabocha squash and simmer until tender, about 10 minutes. Drain well. Transfer the squash to a food processor and puree until smooth.
Place the bread on a rimmed baking sheet; bake for 15 minutes, until just dry.
In a large saucepan, combine the 3 milks with the brown sugar, anise seeds, cloves, cinnamon and allspice and bring just to a simmer, stirring until the sugar is dissolved, about 2 minutes. Whisk in the pureed squash. Strain the mixture through a fine-mesh sieve set over a large bowl; discard the solids. Whisk the butter, egg yolks and vanilla into the mixture and stir in the toasted bread cubes. Drain the prunes, pressing to extract as much of the soaking liquid as possible, then discard the liquid. Add the prunes to the bowl. Let the bread pudding mixture stand for 20 minutes, pressing to submerge the bread and stirring occasionally, until most of the liquid has been absorbed.
Set a 9-by-13-inch baking dish near the stove. In a medium, heavy saucepan, combine the granulated sugar with 1/2 cup of the water and cook over high heat, stirring until the sugar is dissolved. Using a wet pastry brush, wash down the side of the pan to dissolve any crystals. Cook without stirring until a medium-amber caramel forms, about 8 minutes. Immediately pour half of the caramel into the baking dish, swirling it to coat the bottom. Return the saucepan to the heat and add the remaining 1/4 cup of water. Cook until the caramel liquefies, 2 to 3 minutes. Transfer the caramel sauce to a heatproof cup.
Pour the bread mixture into the prepared baking dish and smooth the surface. Bake for about 40 minutes, until the pudding is set and lightly browned. Let cool for 20 minutes. Run a knife around the edge of the pudding, set a cutting board on top and invert. Remove the baking dish and cut the bread pudding into squares. Top with a dollop of crème fraîche, a drizzle of the caramel sauce and a sprinkling of cacao nibs.
Kabocha squash is a sweet-tasting winter squash with pale orange flesh. Cacao nibs are cacao beans without their shells. They're available at specialty food stores and online at amazon.com.