Dissolve the fresh yeast in warm water.

In a large bowl, collect the flour, the sugar, the riced potatoes and the grated zest of a lemon. Pour in the water with the yeast and start kneading using one hand, gradually adding the yolks and the melted butter, and, eventually, the salt.

The dough will be quite sticky, but with some patience – and no extra flour - it will start to come together.

Lightly dust a wooden board. Scrape the dough from the bowl onto the board and knead until it becomes smooth and elastic.

Shape the dough into a ball, lay it in a bowl greased with some olive oil and cover with a damp cloth. Let it rise in a warm place, such as the oven with the little light on, until it doubles. It will take about 2 hours.

When the dough has doubled, lightly flour a wooden board and remove it from the bowl, flatten it lightly, then with a rolling pin roll it to about 1cm thickness.

Using a round cooking cutter, I like to use a 6 cm one, cut out the bomboloni and set them aside.

Knead again what is left after the first bomboloni, roll it out and cut more bomboloni.

Lightly dust with flour the bomboloni, cover them with a cloth and let them raise again.

When the bomboloni are doubled, fill a large pan with frying oil. Be generous with the oil, because the bomboloni have to float, to have that typical lighter line in the centre.

Heat the oil to 155°C-160°C. If you do not have a kitchen thermometer, test the temperature with a wooden spoon. Immerse the spoon handle in the oil: if it will be immediately surrounded by tiny bubbles, the oil is ready to fry.

Fry the bomboloni in batches, for a few minutes per side. When they are golden on one side, turn them gently, let them brown on the other side, then lift them with a slotted spoon and lay them onto a plate lined with some kitchen paper. Sprinkle them immediately with sugar.

Fry all the bomboloni, then eat them as they are or fill them as you prefer: thick custard, chocolate spread, or jam.