Preheat oven to 350°F. Grease a 9 x 13 inch baking dish. Toss the bread cubes, apple slices, and pecans together and spread into an even layer in the baking dish. Set aside.
Combine the heavy cream, milk, and ½ cup sugar in a sauce pan over medium heat. Bring almost to a boil, just until bubbles appear at the edges, stirring occasionally. Meanwhile, whisk the egg yolks and ½ cup sugar in another bowl. When the milk mixture is done, remove from heat and slowly add to the egg yolks (I do this by ladling in a few tablespoons at a time. Continue adding till it is combined.
Pour the custard mixture evenly over the bread cubes, apples, and pecans. Be careful to pour over the top of all exposed bread cubes to prevent them from drying out. Combine the cinnamon and the remaining 2 tablespoons of sugar together and sprinkle liberally over the dish.
Let sit for at least 1 hour, or overnight in the fridge. When ready to bake, do so until the top is golden brown and mixture appears to "puff up" a little out of the pan, 45-60 minutes. Cover with aluminum foil while baking if tops brown too quickly.
To serve, slice and top each serving with a scoop of ice cream and a spoonful of the bourbon sauce.
To make the cinnamon ice cream:
Combine cream and milk in a saucepan over medium heat. Bring almost to a boil, until bubbles appear around the edges, stirring occasionally.
Meanwhile, whisk together the egg yolks and the sugar in a separate bowl. Slowly add the milk mixture to the egg mixture, a few tablespoons a time, until completely combined. Return the mixture to the saucepan and continue to cook over medium heat, stirring constantly to prevent the eggs from curdling, until thickened. Add the vanilla, cinnamon, and bourbon (if using).
Pour into a bowl and chill in the fridge for 2 hours or overnight. When ready, freeze in an ice cream machine according to the manufacturer's instructions, about 30 minutes. Scoop ice cream into another container and freeze for at least an hour to harden before serving.
To make the bourbon sauce:
Combine all ingredients in a medium saucepan over medium heat. Bring to a boil and continue boiling for about 5 minutes until thickened, stirring constantly. Use immediately, or refrigerate.
Note: this is a great do-ahead dessert! If baking ahead of time, store in the refrigerator. When ready to serve, warm in a 350°F oven for about 30 minutes.