To make the dough: Combine 3 cups of the flour, the sugar, salt, and undissolved yeast in a large mixing bowl.

Heat the milk, water, and butter until very warm (120°F to 130°F). The butter doesn't need to melt completely.

Add the liquid ingredients to the flour mixture, along with the eggs.

Beat for 2 minutes; the mixture will be soupy.

Gradually beat in enough of the remaining flour to make a soft dough. In the winter, or under less humid conditions, you may not need all the flour; in the summer, or when it's humid, you'll probably use it all.

Knead the dough until it's smooth, elastic, yet still quite soft, about 6 to 8 minutes. Cover it, and let it rest for 10 minutes.

To make the filling: Whisk together the sugar and cinnamon. Set it aside.

Lightly grease two 9" x 13" pans; or a 9" x 13" pan and two 9" round cake pans.

Divide the dough in half. Working with one piece at a time, pat/roll the dough into a 10" x 15" rectangle. It's a soft dough, and should handle easily.

Spread with half the softened butter (2 tablespoons). Sprinkle with half the cinnamon-sugar.

Starting with a long side, gently roll the dough into a log, pinching the edge to seal as well as you can.

Cut the log into 12 pieces, and space them in the prepared pan.

Repeat with the remaining dough and filling.

Cover the pans, and let the rolls rise until they're nearly doubled, about 1 hour. Towards the end of the rising time, preheat the oven to 350°F.

Bake the rolls for 25 to 30 minutes, until they're golden brown. Remove them from the oven, and cool them for at least 20 minutes before frosting.

To make the frosting: Combine the frosting ingredients, using enough milk to make a soft, spreadable frosting.

Spread the frosting on the rolls. Serve immediately; or cover loosely, and serve later. Store well-wrapped, at room temperature, for several days; freeze for longer storage.

Tips:

If you measure flour the "heavy" way, by dipping your cup into the flour bag, then tapping it to settle the flour and leveling it off (rather than using the "sprinkle and sweep" method), start with 6 1/2 cups flour rather than 7 1/2 cups, and go up from there as needed. Even better — use a scale, and use 32 to 35 ounces flour, enough to make a soft yet workable dough.

If you use vanilla extract in the icing, it'll be cream- to tan-colored, rather than bright white.