1. Make dough: In a saucepan, heat milk over moderately high heat until bubbles form around edge of pan. Remove from heat; add ½ C sugar, ¼ C butter and salt, stirring until butter is melted. Set aside and cool to lukewarm.
2. If possible, check temperature of warm water with a thermometer. Sprinkle yeast over warm water in a large bowl, stirring until the yeast is completely dissolved. Add milk mixture and stir to combine. Add two eggs and 2 C of the flour.
3. Using an electric mixer, beat flour mixture at medium speed for 2 minutes. Add remaining 2 ½ C of the flour and beat with wooden spoon until smooth and dough leaves sides of bowl. Turn onto floured surface and knead until satiny and smooth. About 10 minutes.
4. Place dough in a lightly greased bowl; turn to bring greased side up. Cover with towel; let rise in warm place (85F), free from drafts, until double in bulk (about 1 hour). Punch dough down; turn onto lightly floured surface and knead 10 to 15 times. Shape into 12-inch long roll.
5. Cut roll crosswise into 12 pieces; shape each into a ball. Place on a lightly greased baking sheet, 5 inches apart. With palm of hand, flatten each ball into a 3 inch round. Make topping; Cream, sugar and butter until fluffy; beat in yolk; then blend in flour and cinnamon. Divide into 12 parts.
6. With palm of hand, flatten each piece into a 2-½ inch round. Arrange topping parts on round of dough; score with knife to look like a shell. Cover with towel and let rise until double in bulk (1 hour).
7. Preheat oven to 375F. Bake rolls 15 to 20 minutes or until golden brown. Makes 12 rolls.