Sprinkle yeast over warm water. Add 1/4 tsp sugar and stir to combine. Let sit for 5 minutes to allow mixture to bubble and activate.
In the bowl of stand mixer fitted with a hook attachment, combine dissolve yeast mixture, buttermilk ,eggs, salt and remaining 1/4 cup sugar. Once combined, add 3 cups of flour, 1 cup at at time. Combine to mix and knead until combined. Add butter in three additions. Add remaining 1 cup of flour. Knead until dough is smooth and cleans the sides of the bowl. If dough is too sticky, add flour one tablespoon at a time. (I added 3 Tbsp)
Transfer dough to a lightly greased bowl. Cover bowl with plastic wrap and let sit at room temperature for 60-90 minutes until dough has doubled.
Punch down dough. Divide dough into two equal portions. Transfer to a lightly floured work surface. Roll dough into a 16x12 inch rectangle.
Spread Nutella evenly over the dough, leaving a 1/4-inch border around all the sides. Spread berries over Nutella. Gently press berries into dough. Roll dough into a tight log, starting with the long side. Slice the log into two equal parts. Stretch each log to a length of about 8-inches. Cut one log lengthwise down the middle. Twist the two halves of the dough over each other, making sure the cut side is facing up. Tuck the ends of the dough into itself. Repeat it remaining log.
Place twisted dough into a greased 9"x5" loaf pan. Alternatively, you can also use a 8 or 9-inch cake pan. Simply connect the ends of the twisted dough to create a round shape. Cover with plastic wrap and let bread rise for 45 minutes to 1 hour until the bread has reached the top of the pan.
Meanwhile preheat oven to 350 degrees F. Remove plastic wrap and bake for 35-40 minutes until the internal temperature of the bread hit 185 degrees F.
Let bread sit in pan for 5 minutes before running a knife or offset spatula around the edges to loosen from pan. Let cool for 20-30 minutes before slicing. Serve with additional Nutella and fresh berries.