In a large bowl stir together yeast and the warm water. Let stand for 10 minutes. Stir in evaporated milk, the 1/3 cup sugar, the melted butter, egg, and salt. Stir in 2 cups of the flour. Gradually stir in another 2 cups flour and the 1/2 teaspoon cinnamon to make a dough.
Meanwhile, for topping, in a medium bowl beat the softened butter with an electric mixer on medium speed for 30 seconds. Add the 2/3 cup sugar, beating until well mixed. Stir in the 1 cup flour, the 2 teaspoons cinnamon, and the vanilla.
Punch down dough. Cover and let stand for 10 minutes. Divide dough into 12 portions. Shape each portion into a smooth ball. Place balls about 3 inches apart on parchment paper-lined baking sheets. Press balls down slightly. Divide topping into 12 balls; pat each ball flat. Place one round of topping on each dough ball.
Using a sharp paring knife, cut grooves in topping to resemble the grooves on a scallop shell. Cover rolls and let rise in a warm place until nearly double in size (about 45 minutes).
Meanwhile, preheat oven to 375 degrees F. Bake rolls for 18 to 20 minutes or until light golden brown. Remove from baking sheets. Cool on wire racks. Serve warm or cool.