For the bread:
- 3/4 cup warm milk (about 115 degrees F)
- 2 1/4 teaspoons (1 packet) Red Star active dry yeast
- 6 tablespoons unsalted butter, softened
- 6 tablespoons granulated sugar
- 1 teaspoon vanilla
- 4 egg yolks
- 3 1/4 cups all-purpose flour, plus more for kneading and shaping
- 1/2 teaspoon salt
- Egg wash (1 egg beaten with 1 tablespoon water), for topping
For the filling:
- 1 (13 oz) jar Nutella, or your favorite chocolate hazelnut spread
For the streusel topping:
- 1/2 cup all-purpose flour
- 1/2 cup packed light brown sugar
- 1/4 cup chopped hazelnuts
- 1/4 cup (1/2 stick) cold unsalted butter, cut into 1/4-inch cubes
- In a small bowl, combine warm milk and yeast; stir to dissolve yeast. Let sit 10 minutes until yeast is foamy.
- Meanwhile, in a large bowl or bowl of a stand mixer, beat butter and sugar on medium speed 1 to 2 minutes until light and fluffy. Beat in vanilla and egg yolks, one at a time, beating well and scraping down sides of bowl after each addition.
- Add flour, salt and yeast mixture to bowl; stir just until a dough forms. Using the stand mixer fitted with the dough hook attachment, knead dough on medium speed 4 to 5 minutes, adding a few more tablespoons of flour if needed until a smooth, soft, elastic and only slightly sticky dough forms; OR, turn dough out onto a well-floured surface and knead by hand 10 minutes, adding a few more tablespoons of flour if needed until a smooth, soft, elastic and only slightly sticky dough forms.
- Shape dough into a ball and place in a large, lightly oiled bowl; turn to coat. Cover with plastic wrap and let rise in a warm place 1 hour to 1 1/2 hours until doubled.
- Punch down risen dough. On a lightly floured surface, use a rolling pin to roll dough into roughly an 18-by-18-inch square. Use a spatula to spread Nutella evenly on top of dough.
- Roll up dough tightly like a jelly roll. Use palms to gently roll into a 24-inch (2-foot) long log. Twist log into a figure 8, then twist into a figure 8 one more time, pinching seams to seal. Place dough in a well-greased 9-by-5-inch loaf pan. Cover with plastic wrap or a tea towel and let rise in a warm place 40 to 45 minutes until the loaf just begins to peek over the top of the pan and is nearly doubled.
- Meanwhile, heat oven to 350 degrees F. In a medium bowl, combine all ingredients for the streusel except the butter. Using a pastry cutter or your fingers, cut in the butter until mixture resembles coarse crumbs. Place bowl in refrigerator until loaf is ready to bake.
- Brush the top of the loaf lightly with egg wash. Sprinkle and gently pat as much streusel as you can on top of loaf. Place loaf pan on a baking sheet (to catch any streusel drips), then place baking sheet on center rack of oven. Bake 50 minutes to 1 hour until golden brown and a toothpick inserted in the center comes out clean.
- Remove loaf from pan; transfer to a cooling rack to cool completely before slicing.