Mix all the dry ingredients in a stand mixer bowl. Add the eggs, butter/oil and water and knead for 12 minutes.
Cover and let the dough rise for 10 minutes.
Fold the dough with your hands for a minute, oil it and let it rise until doubled in size, between an hour to 2 hours.
Divide the dough into small balls (25 grams each). Flatten each ball into a circle, place 1 frozen chocolate hazelnut truffle in the center. Fold the dough to close it, tighten and roll into a ball again.
Place the dough balls on parchment paper and spray them with oil. Cover and let them rise for 30 minutes.
Fill ½ a deep frying pot with oil and heat it up on medium heat until you reach 355-375 °F (180-190 °C).
Add each ball into the pot with the closure part facing down. When the donuts turn golden on that side, flip them over and fry until golden all around.
Remove the donuts from the pot, roll the donuts in sugar and cinnamon and serve.