Heat the milk in a small saucepan until it bubbles, then remove from heat. Mix in butter; stir until melted. Let cool until lukewarm.
In a large mixing bowl, combine 2 1/4 cup flour, yeast, sugar and salt; mix well. Add water, egg and the milk mixture; beat well.
Add the remaining flour, 1/2 cup at a time, stirring well after each addition. When the dough has just pulled together, turn it out onto a lightly floured surface and knead until smooth, about 5 minutes.
Cover the dough with a damp cloth and let rest for 10 minutes.
Meanwhile, in a small bowl, mix together frosting ingredients.
Roll out dough into a 12x9 inch rectangle.
Spread dough with half of the lemon frosting. Roll up dough and pinch seam to seal. Cut into 12 equal size rolls and place in lightly greased baking sheet.
Cover and let rise until doubled, about 30 minutes.
Preheat oven to 375 degrees F.
Bake in the preheated oven for 20 minutes, or until browned. Spread remaining frosting over warm rolls.