Heat the Milk, Oil, and Sugar: In a large pot, mix the milk, vegetable oil, and sugar. Heat the mixture on low until warmed through and the sugar is dissolved but do NOT boil. Turn off the burner and remove from heat, make sure the milk mixture is warm but not HOT.
Add Yeast: Sprinkle the yeast on top of the milk mixture and let it sit for one minute.
Add Flour: Add 8 cups of flour to the mixture. Stir it until everything is just combined. Cover it with a kitchen towel and let it sit in a warm place for an hour so the dough will rise.
Add Remaining Ingredients: Add the extra cup of flour, baking powder, baking soda, and salt. Mix thoroughly, scraping down the sides and making sure there are no unincorporated pockets of ingredients.
Chill the Dough: Chill the dough for at least 30 minutes so it's more manageable to roll out or cover it tightly with plastic wrap and leave it for up to 2 days before assembling your rolls.
Make the Base: While the dough is chilling, make the base by mixing together the melted butter and brown sugar until it's thick and dissolved. Pour the brown sugar base evenly into each 9X13 inch pan and spread out so each pan bottom is covered. Set these aside.
Roll the Dough: Place your dough on a liberally floured baking surface, and cut in half. Set one half aside then roll the dough half into a large rectangle, about 1/4 inch thick.
Add Filling Ingredients: Spread softened butter all over the dough, don’t be afraid to use your fingers! Next liberally sprinkle on cinnamon to cover the entire surface of the dough, all the way to the edges. Then evenly sprinkle on one cup of sugar.
Roll It Up: Start from the long side, roll the dough tightly towards the other edge.
Cut the Rolls: Cut the rolls approximately 3/4 inch thick and lay them in the brown sugared baking pan without crowding. (I can usually get 10-12 in each pan).
Let Them Rise: Cover the pans with a clean kitchen dish cloth and let them rise in a warm place for 30 minutes until they are soft and pillowy, then bake at 375°F until light golden brown, about 15-20 minutes. (check your rolls as they cook and cover with foil after the 10 minute mark if they are browning too quickly) Remove from oven when done and place on cooling racks.
Make the Icing: In a large bowl whisk together the powdered sugar, milk, and vanilla extract until smooth. Adjust the milk to get your desired consistency.
Finish the Rolls: When the cinnamon rolls are cooled to room temperature, drizzle with the icing to finish. *Note: Some people like to drizzle the icing on while the rolls are hot, it's totally your preference so feel free to do whatever your heart desires but I prefer the icing set up nicely on the top of my rolls. I also like to bake these for friends & family the night before I deliver them so if they cool overnight, I drizzle the fresh icing first thing in the morning and they look beautiful!