For the crust:
In a large bowl, combine flour, sugar, and salt.
Add butter and use a pastry blender or two knives to work the mixture until it has the texture of coarse oats.
Add water, 1 tablespoon at a time, and mix with a fork until the dough comes together.
Form the dough into a ball and then flatten it into a disk.
Wrap the dough in plastic wrap and refrigerate for at least 1 hour or until chilled.

On a lightly floured surface, roll out the dough to a thickness of about 1/8 inch (3 mm).
Place the dough into a 9-inch (23 cm) tart pan with a removable bottom.
Refrigerate for 30 minutes or until the dough is chilled.
Prick the bottom of the dough with a fork to prevent it from bubbling during baking.
Line the dough with aluminum foil and fill with dried beans.
Bake in the lower third of the oven preheated to 400F (200C) for 15 minutes.
Remove the beans and foil.
Continue baking for an additional 10-15 minutes, or until the crust is golden brown.
Let cool completely on a wire rack.

For the chocolate filling:
In a medium saucepan, heat the unsweetened condensed milk over medium heat until it starts to boil. Reserve.
In a large bowl, whisk together cocoa powder, cornstarch, brown sugar, sugar, malted milk powder, and salt.
Gradually whisk in the 3.25% milk, then the egg yolk, and the reserved condensed milk.

Pour the mixture into the saucepan.
Bring to a boil over medium heat, whisking constantly.
Reduce the heat to low and simmer for 2 minutes, or until the mixture thickens. Remove from heat and whisk in the vanilla extract.
Pour the chocolate filling into the cooled tart shell.
Cover the filling with plastic wrap and refrigerate for at least 4 hours or until chilled.

For the whipped cream filling:
In a bowl, whip the heavy cream until it forms soft peaks.
Add the powdered sugar and vanilla extract, and whip until stiff peaks form. Serve the tart with a dollop of whipped cream.