Place the milk in a small saucepan and heat until steaming. Turn the heat off and add the butter. Once melted, set aside to cool. In a large bowl, combine the flour, yeast, sugar and salt.
Once the milk is lukewarm, add three-quarters of it to the flour mixture with the egg yolks and combine well. Add more milk if needed until the dough comes together and is slightly sticky.
Turn the dough on to a floured surface and knead well for 8 minutes, adding more flour if it begins to stick to the surface. The dough should spring back when poked with a floured finger. Place the dough in a large lightly oiled bowl and cover with clingfilm. Leave to rise in a warm place for an hour or until doubled in size.
Once the dough has risen, knead it again for 1 minute on a lightly floured surface. Divide the dough into 4 equal pieces.
Take 1 piece of the dough (keep the others covered to prevent them from drying out). Roll it out to a disc 2-3 mm thick, keeping it as circular as possible. Place on a sheet of greaseproof paper and, using the base of a 22cm springform tin, make an indentation with the edges of it to create a circle. Spread one third of the Nutella using a cutlery knife to cover the circular area (you might need to put the Nutella in a microwave for 10 seconds to soften it first). Roll out another piece of dough to the same thickness and lay it on top of the previous one and use the cake tin to mark a circle and cover it with another third of the Nutella. Repeat this once more so that you end up with the last layer of Nutella at the top then roll out the last piece of dough and lay it on top of this.
Lay the base of the cake tin on top of the dough and cut around it to remove the excess dough. Using a small round cup or glass, mark the centre of the bread by lightly digging into it with the rim. Divide the cake into quarters and and start cutting with the point of your knife at the marked circle making sure to keep the circle intact. Divide each of these quarters into 4 equal pieces so that you end up with 16 pieces.
Take two pieces of the dough in each hand and carefully twist in opposite directions. Repeat with the remaining pieces and carefully tuck the edges of each piece underneath themselves to give it a rounder edge.
Leave this to prove in a cool place covered loosely with clingfilm for around 30-40 minutes or until slightly puffed up (leaving it in a warm place will cause the Nutella to melt).
Preheat the oven to 200°C/gas mark 6. Once the bread has finished proving, brush it with the egg white and bake for 15-20 minutes or until dark golden and risen.