Step 1
Dissolve yeast in warm water and let sit for 5 to 10 minutes.
Step 2
Meanwhile coat the inside of a large bowl with cooking spray.
Step 3
Add warm milk melted butter egg and salt to yeast mixture; whisk for 1 minute. Gradually stir in flour until dough is no longer sticky.
Step 4
Knead dough by hand on a lightly floured surface or in a stand mixer fitted with a bread hook for 10 minutes. Transfer to the prepared bowl and turn until dough is covered in cooking spray. Cover with a damp cloth and leave in a warm place until doubled in size about 1 hour.
Step 5
Spray a 9x5-inch loaf pan with cooking spray. Mix together sugar and cinnamon in a small bowl; set aside.
Step 6
Remove dough from the bowl. Punch it and fold in the sides. Flatten dough with a rolling pin into a 9x18-inch rectangle. Brush on melted butter and sprinkle with all but 3 tablespoons cinnamon-sugar mixture. Sprinkle with chopped chocolate. Roll dough carefully starting at the short end and pinch closed at the seam. Place seam-side down in the prepared loaf pan. Cover the pan and set in a warm place until doubled in size about 1 hour.
Step 7
Preheat the oven to 375 degrees F (190 degrees C).
Step 8
Brush beaten egg on top of dough and sprinkle with remaining 3 tablespoons cinnamon-sugar mixture.
Step 9
Bake in preheated oven until top is golden brown 40 to 45 minutes. Carefully tip loaf out of pan onto a work surface and let it cool on a wire rack.