In a large, heatproof bowl, lightly beat the egg yolks. Very gradually whisk in 1/4 cup of the hot Champagne caramel until blended. Slowly whisk in the remaining caramel. Set the mixture over a saucepan filled with 1 inch of simmering water. Cook over low heat, whisking constantly, until the custard thickens enough to form a ribbon when it falls from the whisk, about 10 minutes. Remove the vanilla bean. Transfer the custard to a bowl and let cool, then refrigerate until chilled.