The shell is made of traditional Italian pasta frolla (sugar pastry).
Soft, creamy and custardy, it has a subtle sweetness enhanced by warm spices.
For the pastry
- 2 cups + 1 tbsp all purpose flour, sifted, plus more for dusting
- 1 cup icing sugar
- Finely grated zest of 1 unwaxed lemon
- ½ cup + 1 tbsp unsalted butter, chilled and cut into small cubes
- 1 egg plus 1 yolk, lightly beaten
For the filling
- 1½ lb white sweet potato (see Note)
- 1 tsp ground cinnamon
- 1/8 tsp freshly grated nutmeg
- Pinch of fine-grain sea salt
- Finely grated zest of 1 unwaxed orange (optional)
- 3½ tbsp caster sugar
- 2 eggs, lightly beaten
- ⅔ cup whole milk
- ¼ cup grappa (or use freshly squeezed and strained orange juice)
- 1½ tbsp cornflour
- Icing sugar and ground cinnamon, to dust (optional)
Resting time: 30-60 minutes
Preheat the oven to 350°F .
Wash and pat dry the sweet potato.
Cut it into 3–4 large chunks, wrap them in foil and roast until very tender, about 1 hour.
Meanwhile, make the pastry.
Combine the flour, sugar and lemon zest in a large bowl.
Rub the butter into the flour using the tips of your fingers until you have a coarse, crumbly mix.
Add the egg and the yolk, and knead until the dough comes together into a smooth ball — try not to overwork it.
Wrap it in cling film and leave to rest in the fridge for at least 30 minutes, or up to 1 hour.
Remove the sweet potato chunks from the oven and allow them to cool.
Leave the oven on at the same temperature.
Peel and mash the potatoes with a fork, masher or ricer.
Add the mash to a large bowl along with all the other ingredients for the filling.
Stir into a smooth, creamy batter. Set aside.
Roll the chilled pastry into a really thin circle that is large enough to cover a 10 inch loose-bottomed tart tin. (Dust your work surface with flour and move/turn the dough often so it doesn’t stick.
Flip the dough onto the tin using a rolling pin; press it with your fingertips so it sticks to the surface of the tin and cut off any excess.
Pierce the surface all over with a fork, cover with parchment and top with baking beans (or real dried beans, which you can then re-use for this purpose).
Blind bake for 10 minutes.
Remove the base from the oven and then remove the parchment and baking beans.
Pour in the filling and level it.
Return the now-filled tart to the oven and bake for 45 minutes, or until the filling is set and the edges of the crust are deeply golden.
Remove from the oven and leave to cool completely.
If you like, right before serving you can dust the crostata with icing sugar mixed with a generous pinch of ground cinnamon.
The sugar will melt quickly due to the moist nature of the filling, but the cinnamon will leave a warm, spiced imprint that is very pleasant.
This tart is even better the second day as the filling has had the time to rest and set.
• It might be hard to come across the specific sweet potato variety mentioned. If you can’t find it, use a purple-skinned, white-fleshed sweet potato instead.
The only thing to bear in mind is that the filling should be creamy rather than loose.
Strain the potato purée overnight if it looks too wet, then adjust the dose of cornflour to come to the desired thickness.