To make the dough:
Mix the milk, vegetable oil and sugar in a small sauce pan. Warm over medium heat just until the sugar is dissolved and the mixture reaches 95-100°F (lukewarm) on an instant read thermometer. Remove from the heat and pour into a large mixing bowl. Cool, if needed, until the milk reaches 95° to 100° F on an instant read thermometer.
Sprinkle the yeast over the lukewarm milk mixture and set aside for 5-10 minutes. Add 4 cups of the flour and stir until combined (you can do this by hand with a wooden spoon or use the dough hook of a stand mixer). Cover and let rise for one hour in a warm location. The mixture should be bubbly and puffed.
In a small bowl or 1 cup measure, combine the remaining ½ cup of flour, baking powder, baking soda and salt. Stir together until blended. Add the flour mixture to the dough and mix until all flour is incorporated. Cover the bowl and refrigerate overnight, or for a day or two, if desired. If rising for more than a day, watch the dough and punch down if needed to prevent overflowing.
To make the cinnamon rolls:
Grease 3 (9-inch) cake pans with melted butter, set aside.
Heavily flour a large, clean work surface. Lightly punch down the dough and scrape out onto the countertop. Using floured hands, and a floured rolling pin, press and roll the dough into a rectangle at least 30-inches wide and about 18 to 20-inches deep. The dough will be very thin.
Brush 12 tablespoons of melted butter over the surface of the dough, leaving a 1-inch border along the 30-inch side farthest away from you.
Sprinkle ⅔ cup of sugar over the butter layer, followed by the ground cinnamon.
Roll the dough into a log starting at the 30-inch side closest to you. Gently pull the dough toward you, then tuck and roll, and repeat, keeping it pretty tight as you go. Next, pinch the seams to seal.
Using a ruler as a guide, cut the rolls into (30) 1-inch slices. You can use a large, thin, sharp knife to cut the rolls, or a long piece of dental floss works very well, too. Place the rolls, cut side down, into the prepared pans.
Preheat oven to 375° F.
Let the rolls rise in a warm location for 30 to 40 minutes. Once risen, the unbaked rolls should be puffed and smooth. To ensure the rolls have risen properly, gently press the edge of a roll with a knuckle. If the dough does not quickly and completely fill back into the depression, the rolls are ready. Bake at 375° F until light golden brown, about 15 to 20 minutes.
Transfer the pans to a rack to cool while preparing the frosting.
To make the frosting:
Using an electric mixer or whisk, combine the frosting ingredients and blend until smooth. The frosting should be thick, but pourable. Generously drizzle over the warm rolls. Feel free to go little crazy and don’t skimp on the frosting. Serve immediately.