Bring the milk up to a simmer along with the scraped seeds from the vanilla bean (or the vanilla bean paste, if using). In a separate bowl, whisk the egg yolks and sugar. Slowly pour the hot milk into the yolks while whisking constantly, then return the entire mixture to the pot. Cook the custard over medium heat, stirring constantly with a wooden spoon, until the mixture thickens and coats the back of the spoon, about 4 minutes. Strain the custard into a bowl.
Stir the gelatin with 1/3 cup of cool water and let it soften for a minute. Whisk this into the custard while it is still hot. Cool the custard completely to room temperature, then chill the custard for about 15 minutes, so that it is cool to the touch but not setting.
Whip the cream to soft peaks and fold this (using a whisk) into the cool custard mixture. Assemble the charlotte while the custard is still fluid.
Line a 6-cup bowl or charlotte mold with plastic wrap. Slice the jelly roll into 1⁄2 inch slices and line the entire bowl, pressing the jell roll slices together as tightly as possible without altering their shape. Pour the Bavarian cream into the mold and place any remaining jelly roll slices on top. Cover the charlotte with plastic and chill for at least 4 hours to set.
To serve, invert the charlotte onto the serving plate and peel away the plastic wrap. Slice into wedges to serve.