Make the pastry cream: Split the vanilla bean lengthwise and scrape out the seeds with a paring knife. Combine the milk, sugar, vanilla seeds and pod, and the salt in a medium saucepan. Bring to a simmer over medium heat, then remove from the heat.
Whisk the egg yolks in a medium bowl, then whisk in the cornstarch until smooth. Slowly whisk about half of the hot milk mixture into the egg yolk mixture, then pour back into the saucepan with the remaining milk; cook over medium-high heat, whisking, until a few bubbles break the surface and the mixture is thick like pudding, about 2 minutes. Remove from the heat and discard the vanilla pod. Transfer the pastry cream to a bowl; whisk in the butter, then continue whisking until the mixture cools slightly, about 10 minutes. Press plastic wrap directly onto the surface of the pastry cream to prevent a skin from forming; refrigerate until completely cooled, about 1 hour.
Meanwhile make the tartlets: Bake the pastry shells as the label directs; use a fork to remove the centers. Brush the top rim of the shells with the melted butter, sprinkle lightly with the sugar and return to the oven until the sugar is slightly golden, about 5 minutes. Transfer the shells to a rack to cool completely.
Whisk the jelly, brandy, lemon juice and water in a small skillet until smooth. Cook over medium heat, whisking constantly, until thick and bubbling, about 3 minutes. Remove from the heat and let cool slightly, about 5 minutes.
Spoon the pastry cream into the shells. Top with the grapes and drizzle with the jelly mixture.