4 cups (about 1/2 baguette) 1-inch cubes of day-old baguette
1 1/2 cups whole milk
1/2 cup heavy cream
2 large eggs
3/4 cup sugar
1 tablespoon pure vanilla extract
1/8 teaspoon salt
1/8 teaspoon ground allspice
2 tablespoons unsalted butter
1 1/2 cups heavy cream
2 teaspoons cornstarch
1/3 cup sugar
1/3 cup bourbon
Heat bourbon in a medium saucepan over medium-low heat until warm. Pour over raisins in a small bowl; let stand at least 1 hour or overnight.
To make whiskey sauce, bring cream to a simmer over medium heat in a small saucepan. Whisk together cornstarch and 2 tablespoons cold water; slowly whisk into cream. Bring to a boil, whisking constantly. Reduce heat to low; simmer, whisking constantly, 1 minute. Remove from heat; stir in sugar and bourbon. Set aside and let cool completely.
Preheat oven to 350 degrees. Stir together bread, milk, and cream in a large bowl. Whisk eggs, sugar, vanilla, salt, and allspice in a medium bowl; add to bread mixture. Stir in raisins and bourbon.
Melt butter in an 8-inch square baking dish in oven. Remove from oven, and swirl to coat bottom of dish. Pour in bread mixture, distributing raisins evenly. Bake until bread cubes are browned around edges and custard is cooked, about 35 minutes. Let cool completely on a wire rack. Serve with whiskey sauce.