Preparation

• Split the vanilla bean lengthwise and scrape its seeds into a 2-quart saucepan, then add the pod and the milk. Bring to a simmer over medium heat, stirring once or twice with a wooden spoon.
• Meanwhile, whisk the sugar and egg yolks in a medium bowl until the sugar dissolves and the mixture is pale yellow.
• Whisk a little of the hot milk into the yolk mixture to warm it, and then slowly whisk in the rest of the milk. Pour the milk-yolk mixture back into the saucepan, turn the heat down to low, and cook, stirring and scraping into the corners of the pan, until the mixture thickens enough to coat the back of a wooden spoon and holds a trail when you run your finger across it (an instant-read thermometer should register from 170°F to 175°F), about 2 minutes. Immediately strain through a fine-mesh sieve into a medium bowl.
• Fill a large bowl with a few inches of ice water, then set the bowl of crème anglaise into the ice bath to quickly chill it. Stir occasionally until cool, about 5 minutes. Stir in the bourbon. Serve right away or refrigerate for up to 1 week in an airtight container with a piece of plastic wrap directly on the surface of the sauce to prevent a skin from forming.