In the mixer bowl, combine flour, yeast, and sugar with a low-speed whisk.

Mix butter and milk in a separate bowl, gradually adding it to the mixer bowl while whisking. Add the eggs, stir, and incorporate the salt. Continue whisking at low speed until the dough is smooth and uniform, which should take about 10 minutes. The dough should be slightly sticky, and that's okay.

Transfer the dough to a greased bowl, cover it with plastic wrap, and place a towel on top. Allow it to rise for an hour or until it doubles in size.

Using your hands, deflate the dough by removing excess air and divide it into balls weighing 60 grams each. Arrange them in a baking pan with small spaces between them and let them rise again for another 30 minutes.

Preheat the oven to 340°F (170°C) and bake the balls for about 20 minutes.

Remove the baked balls from the oven, cover them with a towel, and let them cool for a few minutes.

Sprinkle powdered sugar, fill each doughnut with Nutella using a syringe or a piping bag, ensuring a pinch of the spread comes out the top. Then, place the hazelnuts on top.