In a small pot off the heat, whisk together the sugar, flour and cornstarch. Add the egg and egg yolk. Mix well. Add the milk, vanilla bean and seeds. Bring to a boil over medium heat, stirring constantly and scraping the bottom and sides of the pot, just until the mixture thickens. Remove from the heat. Pass through a sieve set over a bowl to remove any lumps.
Cover with plastic wrap directly on the surface of the cream. Let cool and refrigerate until step 6.
In a small bowl, combine the egg and cream with a fork. Set aside.
With the rack in the middle position, preheat the oven to 400°F (200°C). Line a baking sheet with a silicone mat or parchment paper.
In a strainer set over a bowl, drain the apricots. In another bowl, combine 24 apricot halves with the sugar. Reserve the remaining apricots for another use.
On a lightly floured surface, roll out the puff pastry to form 2 squares of about 10 inches (25 cm) each. Cut each square into 4 smaller squares. Spread each square with pastry cream, leaving a 1/2-inch (1 cm) border all the way around. Sprinkle the ground almonds over the pastry cream. Arrange 3 apricot halves, rounded side up, diagonally down the centre of each square. Fold the opposite points of the dough over the apricots. Transfer to the baking sheet, spacing them out evenly. With a pastry brush, coat the points and tops of the dough with the egg wash. Sprinkle with sugar.
Bake for 20 minutes or until the dough is golden. Let cool completely on a wire rack.