Preparation: 20'
Waiting: 30'
Baking: 40'-45'
Servings: 6-8
INGREDIENTS
For the dough
250 gr. all purpose flour, sifted
100 gr. olive oil SPARTA WHITE TRUFFLE + 1 tsp.for the baking tray
50 ml milk
1 egg, preferably organic, lightly beaten
1 tsp dried oregano or thyme, grated
½ tsp salt
For the cream
350 ml milk
40 gr. butter
30 gr. all-purpose flour
2 egg yolks
1 small sweet potato, grated on a fine grater
50 gr. sweet gruyere, grated
salt, freshly ground pepper
Some grated nutmeg
For the surface
1 large sweet potato, peeled and cut into thin slices
2 red onions cut into slices
DIRECTIONS
For the dough: Put the sifted flour in a large and deep bowl, add the olive oil and rub the ingredients with your fingers, until you make a mixture that looks like bread crumbs. Add the milk, the egg, oregano (or thyme) and salt and mix all the ingredients together by hand, without too much pressure, until you make a dough that is not necessarily uniform. Shape the dough into a ball, wrap it in a transparent film, and put it in the fridge for 30 minutes before using it. Unroll the dough. On a flat and slightly floured surface, spread it with the pin into a flat dough of 28cm diameter, ie slightly larger than the diameter of the baking tray. Grease the baking tray with 1 tbsp. tablespoon oil and lay the dough in the pan, covering the walls of the pan as well.
For the cream: Heat the milk in a saucepan, without letting it heat too much. In a medium saucepan, heat the butter over medium heat and, when it melts, sprinkle the flour and mix it immediately with the whisk. Cook for 2-3 minutes, until it acquires a dark golden color, constantly stirring with the whisk. Gradually and without stopping the stirring, add the milk. Heat this mixture for a few minutes, without stopping the stirring, until the cream sets. Remove from the heat, add the yolks, the grated sweet potato and the gruyere, season with salt, pepper and a little grated nutmeg and cover the pot with a transparent film, which should be applied on the surface of the cream, so that no crust forms. Leave aside.
For the tart: In a saucepan with boiling salted water, add the sweet potato slices and bake for 3 minutes. Take them out with a slotted spoon and leave them on a plate lined with kitchen paper to dry. Preheat the oven to 180 ° C with air. Pour the cream into the baking pan and flatten it with a spoon. Place the sweet potato and onion slices alternately and in a circle until you cover the entire surface of the cream. Spread with a little olive oil and bake in the oven for 40-45 minutes.