Once the milk/cream/vanilla pod mixture has soaked for 1 hour, place the pot back over medium-high heat, stirring occasionally, and bring the temperature to (185°-190°F/85°-88°C) with an instant-read thermometer. Then, turn the heat to low. (Vanilla pods should still be in the cream/milk mixture.)
Remove the milk/cream/vanilla from the heat and pour a small amount over the whisked egg yolks (Bowl 1), about 1/3 cup. Whisk the egg yolks with the hot cream to temper the eggs.
Once the milk/egg is mixed with the hot milk/cream/vanilla mixture, place back over low heat. Stir constantly until the egg yolks thicken the custard (about 1-2 minutes). Monitor the heat. Do not heat the custard past (195°F/90°C).
To test thickness, dip the spatula or a spoon into the custard mix and draw a line down the center using a finger. Hold the spatula or spoon up sideways and if the custard does not bleed across the line you drew with your finger, it's good to go.
Pour the hot custard over the sieve with the reserved cup of cream (Bowl 2) over the ice bath.
Use a rubber spatula to work the ice cream custard through the sieve.
Use the spatula to scrape the bottom of the sieve into the ice cream custard. Discard the vanilla pods leftover in the sieve.
The ice bath will rapidly cool down the ice cream custard. Once the custard is below (75°-85°F/24°-30°C), add the pure vanilla extract and the bourbon. Stir to incorporate thoroughly. The ice cream custard is now ready for the ice cream machine, or you can store it refrigerated until you need it.