In a medium saucepan, combine 2 cups milk, vegetable oil, and 1/2 cup sugar. Heat until everything just begins to simmer. Stir until sugar is dissolved. Remove from heat and let the liquid cool until it reaches 105 degrees F. Top mixture with yeast and allow to sit for 1 minute.
Put 4 cups flour in a large mixing bowl. (I use my stand mixer with the dough hook attachment, but you can mix with a wooden spoon). Add the milk mixture to the flour and mix until all ingredients are combined.
Cover bowl with a clean kitchen towel and set aside to let the dough rise, for 1 hour.
Add the remaining 1/2 cup flour, baking soda, baking powder, and salt into the dough, and mix to combine. Transfer dough to a lightly oiled bowl, and then place the dough in the fridge for 1 hour, uncovered.
Lightly dust your work surface with flour. Take half the dough and roll it into a 10-inch x 15-inch rectangle. The dough will be pretty darn thin.
Pour 1/2 cup of the melted butter over dough sheet. Use your hands to spread the butter all over the dough.
Mix together 1 tablespoon cinnamon and 1/2 cup sugar. Sprinkle all the sugar mixture evenly over the butter. Use your hands to rub the cinnamon goo all over the dough.
Roll the dough into a log, starting on the short side of the dough. Some filling might ooze out the ends, don't worry about that. Pinch the seam that forms when you're done rolling the dough to seal the dough log. Repeat this process with the remaining half of the dough and remaining filling ingredients.
Using a serrated knife, cut 1/2-inch slices from each dough log. Place slices in four 9-inch non-stick cake pans/pie plates. (If you're not using non-stick pans, lightly grease the pans.) Arrange about 8 rolls per pan with one roll in the center of the rest.
Cover rolls with a kitchen towel (or two), and allow the cinnamon rolls to rest for 20 minutes.
Preheat your oven to 375 degrees F. Bake the cinnamon rolls for 15 to 18 minutes, do not let the rolls overcook and become too browned. Carefully remove from the oven.
While rolls bake, combine icing ingredients in a large mixing bowl until smooth – the icing will look thick. Don't worry, that's okay.
Pour the icing over warm cinnamon rolls, 1/4 of the icing per pan. If needed, use the back of a spoon the spread the icing over the cinnamon rolls.
Allow cinnamon rolls to rest for a few minutes, then serve warm.
Heaping = just over and scant = just under, for this purposes of this recipe.