Step 1

To make the pastry, in the bowl of an electric mixer fitted with the flat beater, beat together the butter and superfine sugar until fluffy. Beat in the eggs and milk until blended. Stir in the flour, baking powder and cornstarch until the mixture comes together in a soft ball. Turn the dough out onto a lightly floured work surface and knead lightly. Divide the dough into thirds. Press each piece into a disk and wrap in plastic wrap. You will need 1 dough disk for this recipe; refrigerate or freeze the other dough disks.

Step 2

Roll out the dough disk between 2 sheets plastic wrap to form a 12-inch round. Remove the plastic wrap from the top and carefully invert the dough into a 10-inch tart pan. Press the dough firmly and evenly into the pan, ensuring that the sides are not too thick. Remove the plastic wrap and run a rolling pin over the top to trim. Refrigerate for 10 to 15 minutes.

Step 3

Preheat an oven to 325°F.

Step 4

Cover the dough with oiled parchment paper or aluminum foil, pressing it evenly into the corners of the dough. Fill with pie weights or dried beans. Bake for 15 minutes. If the paper sticks to the pastry, bake for a few minutes more; it should come off easily. Remove the paper and weights, then continue to bake until the pastry is pale golden in color, 15 to 20 minutes more. Transfer to a wire rack and let cool completely.

Step 5

Increase the oven temperature to 350°F. Brush the inside of the cooled pastry shell with the egg white and bake for 4 to 5 minutes. Transfer to a wire rack and let cool completely.

Step 6

In a saucepan over medium heat, warm the milk to just below a simmer. In a bowl, whisk together the egg yolks, granulated sugar, cornstarch, flour, vanilla, lemon zest and Cognac until smooth. Whisk a little hot milk into the egg mixture, then gradually stir the egg mixture into the hot milk. Cook over medium heat, stirring constantly, until smooth and thickened, 2 to 3 minutes. Remove from the heat and let the custard filling cool for about 1 hour.

Step 7

Spread the custard evenly in the cooled pastry shell. Halve and seed the grapes and place, cut side down, on the custard. Refrigerate for at least 20 minutes or up to 6 hours. Just before serving, in a small saucepan over medium-low heat, gently heat the jelly, then brush over the tart. Serves 10.

Step 8

Adapted from New Healthy Kitchen Series, Desserts, by Annabel Langbein (Simon & Schuster, 2006)