Preheat the oven to 300 degrees F. Grease a 9-by-13-inch baking dish with 1 tablespoon butter.

Toast the bread cubes on a baking sheet until they start to dry and harden, about 20 minutes. Set aside. Raise the oven temperature to 325 degrees F.

Whisk together the cream, milk, sugar, vanilla bean seeds, salt, cinnamon, eggs and yolks in a large bowl. Add the bread to the bowl and stir until completely coated. Cover and let soak for 30 minutes, pushing the bread down occasionally so that it is completely covered.

Pour the bread mixture into the prepared baking dish. Microwave the remaining 2 tablespoons butter in a small microwave-safe dish until melted, about 1 minute. Drizzle the butter over top of the custard and then sprinkle with the turbinado sugar. Bake until the custard is set and the top is golden brown, 1 hour 15 minutes to 1 hour and 30 minutes. Let cool slightly before serving. Serve warm or at room temperature.