For the Dough

• In a medium saucepan, combine the butter, milk, and sugar. Heat over medium-low, stirring occasionally, until butter is melted. (Note: The mixture should only be lukewarm. If it gets too hot, just let it cool off for a couple of minutes before proceeding.)
• Add the instant yeast to the lukewarm butter mixture. Whisk together and set aside momentarily.
• Meanwhile, in the bowl of a countertop mixer fitted with the paddle attachment, add the flour, egg, egg yolks, vanilla, salt and vegetable oil Add the melted butter mixture to the bowl and mix on low speed for 1-2 minutes, or until ingredients come together.
• Increase speed to medium for another 1-2 minutes, or until all ingredients are well combined. (Note: The dough at this stage will be very soft and sticky.)
• Flip dough out onto a lightly floured countertop and fold 3-4 times, rotating the dough 90° after each fold. Place dough in an oiled bowl, cover with plastic wrap, and chill in refrigerator overnight.
• The next day, begin preparing the Chocolate Hazelnut Filling by placing the hazelnuts in a small sheet pan and toasting them in a 350°F oven for 9-10 minutes. While still hot, transfer the hazelnuts into a kitchen towel and rub together vigorously to remove most of the skins. Coarsely chop the hazelnuts and set aside. (Note: The skins come off easier while hot, and the kitchen towel allows you to handle the hot hazelnuts. Don't worry if some skins remain.)
• While the hazelnuts are toasting, heat the 5 Tbsp of butter in a small saucepan over medium-low until melted. Remove saucepan from heat and add the chocolate chips and brown sugar. Stir together until well combined. (The chocolate chips will melt slightly, but not completely.) Add the toasted and chopped hazelnuts and stir until combined. Set Chocolate Hazelnut Filling aside.
• Remove dough from refrigerator and roll into a 10” by 15” rectangle. Spread Chocolate Hazelnut Filling evenly across top of the dough, leaving a ½” border with no filling.
• Beginning with a long edge, roll the dough up into a log, tucking the side edges in as you roll (see picture in post).
• Pinch the seam together, and carefully twist the dough two times (see picture in post) and place into a greased 5" x 9" bread pan. Cover pan lightly with plastic wrap and place in a warm location. Let dough rise for ~1-1½ hours, or until dough just begins to rise over top of the pan.
• Make the egg wash by lightly beating the egg with the milk until well combined. Brush the top of the loaf with the egg wash.
• Bake at 350°F for 30 minutes. Lower oven temperature to 325°F and continue baking for another 15-20 minutes or until top of the bread is golden brown. (Note: If the bread appears to be browning too quickly, place a piece of aluminum foil on top of the loaf after the first 30 minutes). Allow bread to cool for at least 30 minutes before slicing.