In a blender, place flour, salt and cold butter.
Blend to a crumbled mixture.
Add the egg and continue blending until the batter turns to dough.
With your hands, shape the dough to a disc shape and wrap with nylon.
Place the dough in the fridge to set for 1 hour.
In a pan, sauté the onion with the olive oil for 10 minutes, set aside to cool.
Peel and cut the sweet potatoes to round thin pieces.
Cook the cut sweet potatoes in boiling water for 20 minutes, strain the water and set aside to cool.
On a floured surface, roll out the dough to a 3-4 mm thick sheet and set aside the baking pans, making sure to create a right angle between the side and the base, ensuring that the edges remain high.
Stab the dough with a fork.
Freeze the dough inside the pan for an hour.
Preheat the oven to 170°C / 350°F degrees with fan
In a mixing bowl, mix heavy cream, eggs, flour, salt, pepper, nutmeg and thyme.
In the frozen shells, place sautéed onions, cooked sweet potato and pour the filling evenly on top of it.
Bake for 35-40 minutes.
Cool at room temperature.
Have a tartlet and enjoy!