1. Preheat oven to 350 degrees F. Butter a 9x13-inch baking dish.
2. Bring 2 cups of water to a boil in a small saucepan. Place golden raisins in a bowl and cover with boiling water. Let sit for 10 minutes then drain and discard the water. (This step plumps up the raisins, making them juicier and softer instead of chewy. I do this anytime I'm baking with raisins.)
3. Toss bread cubes and plumped raisins together in a large bowl.
4. In a medium saucepan, whisk together the milk, sugar, cinnamon, nutmeg, and cardamom. Add butter and heat over medium-low heat until butter has melted and milk is warm, but not boiling. Remove from heat and whisk in vanilla and beaten eggs.
5. Pour egg mixture into the bowl of bread cubes and raisins. Gently stir the bread until all cubes have been coated with the egg mixture. Let sit for 5 minutes.
6. Transfer mixture to prepared baking dish. Sprinkle brown sugar over the top. Bake uncovered for 35-40 minutes, or until custard is set in the center and the top is lightly golden.
7. Serve immediately with vanilla sauce.

Prepare the Warm Vanilla Sauce:

1. In a medium saucepan, whisk together the sugar, flour, and heavy cream. Add butter and heat until boiling, whisking frequently. Let simmer for a few minutes until sauce has thickened to your desired consistency. Remove from heat and stir in vanilla. Keep warm until ready to serve.