Prepare the pans. Butter two 9 inch by 5 inch loaf pans, layer the bottom with parchment paper, and grease the paper.
Divide the babka dough in half and put one half back in the bowl. Lightly flour the countertop and roll out the other half of the dough into a rectangle about 12 inches by 14 inches.
Use an offset spatula or knife to spread half of the Nutella onto the surface of the rectangle, leaving about half inch on all edges.
1 cup (280 grams or 10 ounces) Nutella
With the long side facing you, dab a small amount of water along the far edge of the rectangle. Roll the rectangle up into a roulade that will be about 14 inches long.
Place the roulade seam side down onto a baking sheet and press down lightly to seal. Freeze for 10 to 15 minutes.
Using a sharp knife, cut the roulade in half lengthwise. You will have two halves about 14 inches in length.
Lay the two halves on your countertop with the inside facing up and pinch the tops together.
Twist them together by lifting one side over the other and repeating, always keeping the cut side of the halves facing up, until you have twisted the full length. Pinch the bottom of the halves together.
Carefull transfer the twisted babka to the prepared pan, cover it with plastic wrap, and let it rise in a warm place until it doubles in volume and reaches the sides of the pan, about 2 to 3 hours. Repeat with the second babka.
When almost ready to bake, preheat the oven to 375°F.
Bake for about 40 to 45 minutes, until the top of the babka is a golden brown and a toothpick inserted inside comes out clean.
Meanwhile, make the sugar syrup by combining the sugar and water together over a boil until the sugar has dissolved.
⅓ cup water, ⅓ cup (67 grams or 2.4 ounces) granulated sugar
When the babkas have baked, place the pans on a cooling rack and brush with the sugar syrup.
Let cool for about 10 minutes, then remove from the pans and let cool before slicing. Once cool, baked Nutella babka can be frozen or wrapped and stored at room temperature for several days.