Tangzhong:
6 tablespoons milk, preferably whole
2 tablespoons AP flour
Dough:
1 cup starter
1/4 cup sugar
1 teaspoon salt
1 tsp. dry yeast
1/2 cup milk, preferably whole
2+ cups AP flour
Filling:
1 stick very soft butter (4 oz.)
3/4 cup brown sugar
4 tsp. Cinnamon
Icing:
6 oz. Cream cheese, softened
2 cups powdered sugar
2 T. Milk or cream
9x13 casserole dish, 10x15 jelly roll pan, or 12 inch cake pan
Oiled container
Kitchenaid mixer with dough hook
Cinnamon roll dough using Japanese Milk Bread From Starter/discard as its base. This makes for pillowy rolls.
Make the tangzhong: Combine the ingredients in a small saucepan, and whisk until no lumps remain.
Place the saucepan over low heat, and cook the mixture, whisking constantly, until it forms a thick paste. Remove from heat, scrape together and let cool.
Combine the tangzhong, starter, sugar, salt, yeast, and milk. Incorporate the flour and knead on medium speed for five minutes.
Incorporate more flour, a tiny amount at a time, and continue to knead, until a ball forms that pulls away from the sides. It will still be stuck to the bottom.
Turn out onto a lightly floured board. Shape into a nice ball and move to a lightly oiled container.
Cover and let rise until doubled, up to 4 hours, or put it in the fridge overnight.
Pull the dough out and let it sit at room temperature until it has warmed and appears doubled if you refrigerated it.
Mix your filling ingredients. Line your pan with parchment and lightly oil the edges.
Turn dough out onto a lightly floured board. Divide into two equal sized balls.
One at a time, roll each out to 12 inches, spread on half the filling, and roll up.

Gently pinch the seam into the roll.
Cut each into six pieces about 2 inches long.
Line the rolls up inside your pan and push down very gently. Cover tightly with plastic wrap (don't skip this step, it forces the rolls to rise out instead of up) and let rise until fluffy and just touching, about 1-3 hours.

Preheat the oven to 325°F.
Bake for 25-30 minutes, until golden brown on top. 
Transfer to a cooling rack and make your icing.
Mix the cream cheese and powdered sugar until smooth. Scrape the bowl as needed. Add milk or cream and whip together.
Let the rolls cool a bit, and spread with the icing or pull apart and spread with icing individually.
If you are making these a day ahead, let the rolls cool in the pan and cover with plastic wrap without icing them. The next day, put the pan in the oven on low heat until they are warmed through, then ice.
With dry yeast: Replace the starter with 1 cup of flour, 1 cup of water, and 1 T. of dry yeast. Let sit 15 minutes, then continue with the recipe as written.
Japanese Milk Bread From Starter/discard
*This dough is a very slow riser. Even after sitting in the refrigerator overnight, you may find that it has barely moved. To speed things along, put the dough someplace warm. You can even use a space heater, just don't put the dough too close or you will kill the yeast.
*You can replace the cream cheese in the icing with butter or do half and half.