In a large bowl stir together yeast and warm water, let stand for ten minutes.
2 1/4 teaspoons active dry yeast, 1/2 cup warm water
Stir in evaporated milk, 1/3 cup sugar, melted butter, egg, and salt. Stir in 2 cups flour. Gradually stir in remaining 2 cups flour and the 1/2 teaspoon cinnamon to make the dough.
1/2 cup warm evaporated milk, 2.6 ounces granulated sugar, 1/3 cup butter, 1 egg, 1 teaspoon salt, 19.3 ounces all purpose flour, 1/2 teaspoon ground cinnamon
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 the 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. It may be easier to do the final mix with your hands, bringing the mixture together to the consistency of playdough.
1/2 cup butter, 5.1 ounces granulated sugar, 4.8 ounces all purpose flour, 2 teaspoons ground cinnamon, 1 teaspoon vanilla extract
Punch down the dough then cover and 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 using the palms of your hands. Or, form the balls place between parchment paper to roll flat into a 3 inch circle. Place one round of topping onto each dough ball, pressing slightly into the sides of the dough balls to help it stick.
With a light hand, use a sharp paring knife to gently cut grooves in the topping to resemble a scallop shell. You do not need to score deeply. 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.
Be sure to check the expiration date on your active dry yeast before beginning.
You can use salted or unsalted butter here, depending on your preference.
It's important to use properly warmed water when proofing yeast, aim for 115-120F. We're also adding warmed evaporated milk. It's warmed to the same temperature so that it doesn't slow down the yeast activation.