Mix the packet of yeast into the warm water and let sit for about 5 minutes until frothy.
In a glass bowl, mix the flour and sugar together. Mix in the milk and then the yeast mixture. Pour into a gallon ziplock bag and leave it out on the countertop.
For the next 5 days, be sure to mash the ziplock bag around, encouraging the yeast to activate.
On the 6th day, add 1 cup of flour, 1 cup of sugar, and 1 cup of milk to the ziplock bag. Close and mash around until all are combined.
Continue to mash around once a day for days 7-9. On the 10th day, your starter is ready for baking or gifting. Reserve 1 cup for baking, 1 cup for gifting. If you would like to keep the starter going, add 1 cup flour, 1 cup sugar, and 1 cup milk to the remaining starter and mix around. This starts the cycle over again and day 10 becomes day 1.
Preheat oven to 325°. Grease two 9x5 loaf pans and set them aside.
In a glass bowl mix the starter, oil, granulated sugar, eggs, and vanilla together. In another bowl mix the baking powder, baking soda, salt, cinnamon, and flour together.
Pour the liquid mixture over the dry ingredients and stir to combine.
Fill the two prepared pans with ¼ of the batter, using half in total. Mix together the cinnamon and sugar and sprinkle half of it over the top of the batter in the pans. Split the remaining batter evenly between the two pans and sprinkle the remaining cinnamon sugar over the top.
Bake for 40-50 minutes, or until a toothpick comes out clean. Allow cooling in the pan.