Stir the yeast into warm water in a large mixing bowl and let stand 5 minutes. Heat milk and butter until warm (100° to 110°F) and add to bowl. Add 1 cup flour, sugar, cocoa, salt, egg, egg yolk and vanilla. Beat for 2 minutes with electric mixer until very smooth. Add enough of the remaining flour to make a soft dough. Turn out onto a lightly floured surface and knead about 8 to 10 minutes, until the dough is smooth and elastic. Place dough in a large greased bowl, cover and let rise about 1-1/2 to 2 hours, or until dough has doubled in size.
Punch dough down. On a lightly floured surface, roll dough into a 15 x 10-inch rectangle. Spread with softened butter. Combine brown sugar and cinnamon and sprinkle over butter. Roll up from long sides like a jelly roll. Cut into 12 equal pieces. Arrange rolls, cut sides up in a greased 13 x 9-inch pan.
Cover pan loosely with greased plastic wrap and let rise until doubled, approximately 1 hour.
While rolls are rising, prepare frosting. Combine evaporated milk, sugar, egg yolks and butter in a large saucepan. Cook over medium low heat, stirring constantly until mixture is thick and comes to a boil. Remove from heat and stir in vanilla. Add nuts and coconut. Refrigerate until ready to frost rolls.
Bake in preheated 350 F oven for 25 to 30 minutes or until lightly browned. Remove from oven and cool on wire racks for 20 minutes.
Spread prepared frosting over rolls and serve immediately.