Tart Dough

1. In a large bowl whisk together flour, sugar, and salt.  Add in the cold diced butter and rub the butter and flour together between your hands until the butter is broken down into smaller pieces and the mixture resembles coarse crumbs.  Make a well in the center in the center of the flour and pour in the whisked egg yolk.  Use a fork to mix the egg yold into the flour.  Add in 2 tbsp cold water and use your hands to bring the dough together.  Add in a few more drops of water at a time, if needed, to allow the dough to come together.
2. Turn the dough out onto a clean surface and gently gather together to form a smooth ball.  Flatten the ball into the shape of a disc and cover tightly with plastic wrap.  Refrigerate for at least 1 hour.
3. Let the chilled dough sit at room temperature for 10-15 minutes to soften slightly.  On a floured surface, roll dough into an 11-12 inch circle.  Place the dough into a 9-inch round fluted tart pan with a removable bottom.  Gently lift the dough and press it into the bottom and fluted sides of the pan.  Use a sharp knife to cut away any excess dough.  (Alternatively, run the rolling pin over the top of the pan to trim away the excess dough.)  Loosely wrap in plastic wrap and freeze the tart dough for 30 minutes. 
4. Preheat the oven to 375°F.  Prick the bottom of the chilled tart all over with a fork.  Line the tart with crumpled up parchment paper and fill evenly with pie weights.  Place tart on a baking sheet and bake for 18-20 minutes, until the shell is golden and set.  Remove from the oven and set aside on a wire rack.  Allow to cool for a few minutes before carefully removing the parchment paper and pie weights.  (Tart shell must be warm when adding in the filling).

Filling

1. While the crust bakes, whisk together sugar, eggs, cornstarch and salt in a bowl.  In a saucepan, bring the milk and cream to a simmer over medium heat.  Slowly whisk about 1 cup of the hot milk into the egg mixture to temper the eggs.  Add the tempered egg mixture into the remaining hot milk in the large saucepan.  Cook over a medium heat, whisking continuously, until the custard has thickened, begins to bubble, and reaches 180°F (it should be the texture of pudding).
2. Remove from the heat and use a fine mesh sieve to strain into a clean large bowl.  Stir in the vanilla extract.  Pour filling into the warm tart shell until it is slightly below the top.  (You may have extra filling left over.*)  Smooth the top of the custard with a clean spatula into an even layer.
3. Lower the oven temperature to 350°F and bake the filled tart for 15-18 minutes.  The edges of the filling should begin to set but the center will still be wobbly.  The tart will continue to set up fully as it cools.
4. Allow to cool completely on a wire rack for several hours.  Cover loosely with plastic wrap and refrigerate for a few more hours, or overnight, until thoroughly chilled.  If needed, blot the surface of the chilled tart gently with paper towels to remove any excess moisture.  Sprinkle 3 tbsp granulated sugar evenly across the top of the tart.  Use a kitchen torch to caramelize the sugar until it turns a golden brown color.  Serve immediately.