Reserve 1/4 cup evaporated milk. Add water to remaining milk to make 1/2 cup. Combine with sugar, salt, and egg yolks in a large mixer bowl. Beat well. Add butter and 2 cups of flour. Beat until smooth. Sprinkle yeast into warm water; stir until dissolved. Add yeast and 1 more cup of flour to the first mixture. Beat at medium speed for 3 minutes. Blend in remaining 1.5 cups flour. Cover, and let rise until double. Heat reserved 1/4 cup evaporated milk in the microwave, just to boiling. Add chocolate pieces and cinnamon, and stir until smooth. Cool to room temperature. Punch down dough. Turn out on well-floured surface. Knead lightly a few times, and roll into a 10" by 15" rectangle. Spread with chocolate mixture; roll up from long side like a jelly roll. Place roll seam side down in greased pan. Press ends together to seal. Sprinkle with the topping mixture. Cover; let rise in a warm place until double in bulk. Bake for 45 minutes.
This cake freezes quite well and remains fresh at room temperature for about 3 days. It's a beautiful and delicious cake to serve for a brunch.