3 1/2 sticks unsalted butter, at room temperature, plus more for greasing
For the salted caramel whisky sauce:
1 stick unsalted butter, cut into pieces
1 cup plus 2 tablespoons sugar
2 teaspoons sea salt
21/2 cups heavy cream
1/4 cup Irish whisky
Preheat the oven to 400°F and grease an 8 1/2-inch square nonreactive baking dish.
In a medium-size mixing bowl, combine the golden raisins and whiskey, and let soak for one hour.
In a large bowl, beat together the eggs, cream, sugar, spices and vanilla to make a custard. Spread one side of each slice of bread with the butter. Cut the slices in half diagonally and arrange half of the bread in the bottom of the baking dish, overlapping the slices. Drain the raisins and sprinkle half over the bread. Repeat with the remaining bread and raisins. Pour the custard over the bread and let soak for 30 minutes.
Place the baking dish in a large baking pan. Add enough hot water to come halfway up the sides of the dish. Bake in the oven for 50 to 60 minutes, or until the pudding is set and the top is golden. Remove the baking dish from the water bath and let cool slightly on a wire rack.
Make the salted caramel whiskey sauce: In a small saucepan, melt the butter over medium heat. Beat in the sugar, sea salt, cream and whiskey. Reduce the heat to low and simmer until the sauce thickens, about ten minutes. Serve the pudding warm with the salted caramel whiskey sauce spooned over each serving.