Using a food processor, pulse together the flour, sugar and salt until combined. Add butter and pulse until mixture becomes coarse meal, about 15 pulses.
In a small bowl, combine egg yolk, water and vanilla extract. Add the egg mixture to food processor and pulse until it starts to clump together. DO NOT pulse until ball is formed. It should be crumbly with large clumps of dough.
Turn dough only a lightly floured surface and form into a ball. Flatten slightly to form a disk. Wrap in plastic wrap and put in fridge for at least 1 hour or up to 3 days.
If using mini tart shells, divide dough into 6 equal balls. On a lightly floured surface, roll each piece of dough into a circle slightly larger in diameter than the tart shell. Press dough into each tart shell, trimming the edges with a sharp knife. Cover each with plastic wrap and place in fridge for at least 30 minutes or until firm. NOTE - If using a 9 inch tart shell, just roll out to diameter slightly large and repeat steps above.
Preheat the oven to 375°F. Prick the bottom of each tart with a fork 2 or 3 times. Bake the shells for 25 minutes until golden brown, not dark. Rotate the tart halfway through. Remove the tartlets from the oven and let them cool completely.
Caramel Filling
Place the cream and butter in a small saucepan over low heat and warm until the butter has melted and set aside.
Place the sugar and water in a medium saucepan over low heat and cook, stirring, until the sugar is dissolved. Put a sugar thermometer in the pan and increase the heat to high. Bring to the boil and cook for about 10 minutes, without stirring, or until the temperature reaches 340°F and the mixture is a deep caramel color.
Remove from the heat and working quickly, add the cream and butter mixture and whisk to combine (be cautious here as it will bubble up). Return to the heat and cook for another 5 minutes or until thickened slightly. Stir in salt.
Pour caramel mixture into pastry shells and place in fridge for at least 30 minutes or until set.
Chocolate Ganache
Place chocolate in a medium bowl. Heat the cream in a small saucepan over medium heat until it begins to simmer. Pour cream over chocolate. Let sit for about 2 minutes and then stir until the chocolate is completely melted and smooth. Pour over each tart until smooth and caramel is completely covered. Place back in fridge for 30 minutes or until set. Sprinkle some salt over tart and serve cold.
Notes
The homemade tart crust is actually super easy to make and you will notice the difference. But you can skip and use store-bought pie crust if needed.
Use a candy thermometer so you know when your caramel is ready to have the cream added. Once it reaches 340°F, it is ready.
Use quality dark chocolate as it contributes to the flavor of the tarts.
You can store the caramel tart in an airtight container for a week in the fridge or 3 months in the freezer.