Mix the dry ingredients

• In a mixing bowl, combine the all-purpose flour, sugar, powdered milk, instant yeast, bread improver and salt.
• Whisk briefly so everything is evenly distributed.

Add the wet ingredients

• Add the egg yolk and cold water to the dry mixture.
• Mix until a shaggy dough forms, adding a little more water if the flour absorbs more than expected.

Knead in the butter

• Add the soft butter and knead until the dough is smooth, soft and elastic.
• The dough should pass a light windowpane test.

Let the dough rise

• Shape the dough into a ball, cover and let it rise until doubled in size.

Divide and shape

• Punch down the dough and divide it into 12 pieces of about 40 g each.
• Roll each piece into a smooth ball and place on a lined tray.
• Cover and let them proof until puffy.

Fry the donuts

• Heat the frying oil to about 160–170 °C.
• Fry the donuts in batches until golden on both sides.
• Drain on a cooling rack or paper towels and let cool completely.

Fill with Nutella

• Fill a piping bag with the Nutella.
• Poke a small hole in the side of each donut and pipe in the Nutella.
• Serve the donuts fresh.