• Cook potatoes in pot of boiling salted water for 15 to 20 minutes or until tender. Pass through ricer while still warm; set aside. In small bowl, combine milk, sugar and yeast. Let stand for 5 to 10 minutes or until foamy.
• In large bowl, whisk together flour and salt. Using wooden spoon, stir in potatoes, yeast mixture, egg, egg yolks and extra virgin olive oil until dough starts to form (or mix in stand mixer with dough hook attachment).
• Transfer to lightly floured work surface. Knead until dough is smooth and elastic, adding up to 2 tbsp more flour if necessary. Place in greased bowl, cover and let stand for 1 1/2 to 2 hours or until dough is doubled in volume.
• On lightly floured work surface, roll out dough until 1/2-inch thick. Using 3-inch round cookie cutter, cut out 16 donuts, rerolling scraps as needed. Transfer to lightly floured parchment paper–lined baking sheets, spacing at least 2 inches apart. Cover and let stand for 45 to 60 minutes or until donuts have doubled in volume.
• Pour enough extra light olive oil into straight-sided saucepan to come 3 inches up side; heat over medium heat until deep-fry thermometer registers 375˚F. Gently drop in donuts; deep-fry for 3 to 4 minutes or until golden brown, turning halfway through cooking time. Drain on paper towel. Let cool completely.
• Fill piping bag with chocolate hazelnut spread fitted with plain tip. Pierce hole in top center of the cooled donuts; fill with chocolate hazelnut spread. Dust with icing sugar.

Tip: Alternatively, fill donuts with jam or jelly instead of chocolate hazelnut spread if desired.