In a medium saucepan over medium-low heat, combine heavy cream, milk, and 2 1/2 Tbs (30 g) sugar. Split and scrape vanilla bean into mixture. Heat, stirring often, until sugar is dissolved and hot to the touch, about 15 minutes. Remove from heat, cover, and let steep for an hour.

Strain cream mixture to remove vanilla pieces, and return to the saucepan. Heat over medium-low heat until warm, stirring often.

In a medium bowl, whisk together egg yolks and 2 Tbs (25 g) sugar. While whisking, slowly add warm cream mixture to temper the yolks. Return the mixture to the saucepan and place over medium low heat and warm to about 130°F.

Place chocolate in a medium heat-proof bowl and pour the hot cream mixture over the chocolate. Whisk until melted.

Strain mixture into something with a pour spout. You should have 2 cups of liquid. Divide among 4 custard cups and place custard cups in a baking dish.

Preheat oven to 300°F and bring a large kettle of water to a boil.

Place baking dish in the oven, and pour boiling water into the baking dish to bring water 2/3rds up the sides of the custard cups.

Bake for about 30 to 35 minutes, or until the custard jiggles (like jello) when the cups are moved.

Remove cups to a cooling rack and let cool completely. Refrigerate 8 hours before serving.