Step 1Whisk the egg yolks lightly to break them up in a large bowl. Set aside.
Step 2Scald the cream and milk in a large, heavy saucepan. Keep warm over low heat.
Step 3Heat the sugar and vanilla bean in a small heavy saucepan or an unlined copper pan over medium heat until the sugar caramelizes, 5 to 8 minutes. Stir occasionally with a wooden spoon to ensure that the sugar colors evenly. Once one portion of the sugar begins to darken, toss it with the uncooked sugar. This will prevent the sugar from burning in one spot before the entire mixture has liquefied and turned a dark caramel color.
Step 4When the mixture begins to smoke, set the bottom of the pan in a bowl of water to stop it from cooking and coloring further. Remove the vanilla bean. Immediately begin whisking the mixture into the warm cream in 3 or 4 batches; pour in the cream quickly or it will continue to cook and burn. (Careful -- it will splatter and bubble up.) Reheat the cream mixture, stirring constantly, until the caramel is completely incorporated.
Step 5Pour about one-fourth of the hot cream mixture into the egg yolks, whisking continuously. Return to the saucepan, and whisk together with the remaining cream. Cook over low heat, being careful not to boil, stirring constantly with a wooden spoon, until the mixture thickens enough to coat the back of the spoon, about 5 minutes. Strain through a fine-mesh strainer into a bowl. Whisk a few times to release the heat. Chill about 1 hour.
Step 6Freeze in an ice cream machine according to the manufacturer's instructions.