For the creme brulee: In a medium saucepan, bring the cream, sugar and vanilla bean to a boil. Add the egg yolks and continue to cook, whisking until slightly thickened. Remove the pan from the heat, strain and set aside for later use.
For the caramel: Stir together the milk and sugar in a large, heavy-bottomed pot. (Make sure the liquid only goes three-quarters of the way up the sides, as it will froth when the baking soda is added.) Add the vanilla extract, salt, cinnamon stick and vanilla bean with seeds if using. Heat the mixture over medium-high heat, constantly stirring, and bring to a boil, about 15 minutes. Keep your eyes on the pot-- it boils over easily and quickly! Quickly remove from the heat and add the baking soda to the pot. The mixture will rise and become frothy, just keep stirring the mixture.
Return the pot to medium heat, and stir frequently, about every 10 minutes. Make sure the milk stays at a gentle simmer rather than a raging boil, and stir across the bottom of the pot to make sure the mixture is not scorching. Adjust the heat as needed. Cook until the milk starts to turn golden brown, about 1 hour 30 minutes.
Remove the cinnamon stick and the vanilla pod. At this point, it will start to thicken quickly, so it's important to keep stirring so the milk doesn't burn on the bottom of the pan. Keep stirring until the mixture is a rich brown and thick enough to coat the back of the spoon, 15 to 30 minutes.
Cool the sauce slightly and then pour into an airtight container. Store the mixture in the refrigerator for up to 1 week.
Preheat the oven to 300 degrees F.
Using a melon baller, hollow out the crab apples. Fill the centers with the creme brulee and bake until the creme brulee is set. Chill overnight.
Reheat the caramel until soft enough for dipping. Dip the stuffed apples using a stick or fork. Chill for 1 hour before serving.