In a large bowl stir together yeast and warm water, let stand for ten minutes. Stir in evaporated milk, 1/3 cup sugar, melted butter, egg, and salt. Stir on 2 cups flour. Gradually stir in remaining 2 cups flour and the 1/2 teaspoon cinnamon to make the dough.
Turn dough out onto lightly floured surface. Knead 3-5 minutes, until smooth and elastic. Shape into a ball and transfer to a greased bowl, turn he dough to coat. Cover and let rise until doubled, about 60-75 minutes.
Meanwhile, for the topping, in medium bowl, beat softened butter with mixer on medium for 30 seconds. Add 2/3 cup sugar, beat until well mixed. Stir in 1 cup flour, 2 teaspoons cinnamon, and vanilla.
Punch down the dough then cover an let stand ten minutes. Divide dough into 12 pieces. Roll each piece into a ball and place 3 inches apart on a parchment lined baking sheet. press balls down slightly. Divide topping into 12 balls, pat each ball flat. Place one round of topping onto each dough ball.
Use a sharp paring knife to cut grooves in the topping to resemble a scallop shell. Cover rolls and let rise until doubled, about 45 minutes.
Meanwhile, preheat oven to 375 F. Bake rolls 18-20 minutes, or until light golden brown. Remove from baking sheet and cool on wire racks.