Nutella & Hazelnut Babka

For the Babka:
2 tablespoons instant yeast
3/4 cup lukewarm milk
6 tablespoons salted butter, room temperature
6 tablespoons sugar
1 teaspoons pure vanilla extract
4 egg yolks
3 1/3 cup all-purpose flour
1/2 teaspoon salt

1 egg lightly beaten PLUS 1 tablespoon water to egg wash top of loaf

For the Filling:
one 13-ounce jar Nutella
1/2 cup toasted hazelnuts (with skins removed), coarsely chopped

For the Streusel:
1/4 cup cold salted butter, cubed
1/2 cup all-purpose flour
1/2 cup brown sugar

Directions

Sprinkle the yeast over the warm milk in a small bowl. Stir and set aside for about 5 minutes or until the yeast is starting to foam and get a bit bubbly.  Meanwhile, in a stand mixer fitted with the paddle attachment, whip the butter until light and fluffy. Add in the sugar and continue beating on medium speed until again, light and fluffy.  Beat in the vanilla and the egg yolks, one at a time, beating well between each addition.  Remove paddle attachment and replace with the dough hook. Add the salt and flour.  Mix to combine and then add the milk and yeast mixture.  Bring the dough together on the lowest speed, then allow it to knead on speed 2 for about 4 minutes. You should have a soft and golden coloured dough.  Place the dough into a greased bowl, cover with plastic wrap and allow to rest in a warm place until almost doubled, about an hour to an hour and a half depending on the temperature of your kitchen and the quality of the yeast. 
 
Once the dough has risen, roll out into a 15" circle/square on a lightly floured surface. OR as close as you can get to either. Mine was a bit of a morph between the two. Just get it big and flat and around 15" wide.  Spread the entire jar of Nutella onto the top of the dough, leaving 1/4" boarder. I used an offset spatula to make this step easier. Then sprinkle with the toasted hazelnuts.  Roll the dough up tightly like a jelly roll. Using a sharp, long knife, slice the roll lengthwise into two sections.  Twist the two sections together (I pinched the ends to keep the twist in place as it will try to unravel itself).   Roll the twist into a tight spiral. 
 
Turn the spiral onto its side and place upright into a greased pan lined with parchment paper. Press down lightly to help take the shape of the pan. Cover with a lightly greased piece of plastic wrap and allow to rise again until the dough takes the shape of the pan, about 1 hour. *Put in a warm, dark place such as the oven or microwave if you live in a dry climate.
 
Once the dough has risen again, prepare the struseul topping. Place the butter, flour, and brown sugar inside a food processor.  Pulse the mixture until it resembles coarse sand. Poke Babka a few times with a toothpick and use a pastry brush to cover the top with the lightly beaten egg/water mixture.  Cover with the struseul topping, pressing down lightly to help stick.  Bake in a preheated 350 degree F oven for 50 minutes. Once you are able to handle the Babka, remove from pan and continue to cool on a wire rack. 
 
 Babka recipe adapted from Mmm...is for Mommy
technique from Simplesmente Delicia