In a large bowl, whisk together 7 cups all-purpose flour, 1/3 cup granulated sugar, 3/4 teaspoon baking soda, 2 teaspoon salt and 1 tablespoon yeast. Set aside.
In a small saucepot over medium heat, warm 2 1/3 cups eggnog to lukewarm in order to activate your yeast. You want the temperature to be between 95 and 115 degrees (F) — any more than that, and you'll kill the yeast. A good rule of thumb is to stick your finger in the eggnog — you want the temperature to be similar to that of a pleasant, warm (but not HOT) bath.
Once the eggnog has been warmed, remove from heat and transfer to a medium bowl. Whisk the eggnog continuously while adding 2 large eggs and 1/2 cup vegetable oil. Set aside.
Use a tall cup or a large measuring cup to make a well in center of the dry ingredients (from the 1st step) and add liquid ingredients (from the 3rd step), using a wooden spoon or rubber spatula to stir until combined. As the dough starts to form, transfer to a lightly floured counter and knead for 10 minutes until the dough is smooth and elastic. If the dough is sticking, you can add up to 1/2 cup of extra flour as you knead, but don't over do it — too much flour will lead to a bread that's too heavy and dense.
Transfer the dough to a greased bowl, cover with plastic wrap, and store in the refrigerator for at least 6 hours, preferably overnight. During this time, the dough will double in size.
Once the dough has doubled in size, start to prepare the filling. In a small saucepot over medium heat, melt 1/3 cup cubed unsalted butter, constantly whisking. Stir as it bubbles, and after 2 to 3 minutes you should see brown bits appear on the bottom of the pan. Remove from heat immediately and continue to whisk for another 30 seconds or use. Set aside to cool slightly as you roll out the dough.
Remove the chilled, proof dough from the refrigerator and transfer to a lightly floured counter. Use a rolling pin to roll the dough into a rectangle about 16 x 24 inches.
Use a pastry brush to brush the rolled dough with 1/3 cup melted unsalted butter (from the 6th step). Sprinkle heavily with a mixture of 3/4 cup brown sugar, 1 tablespoon ground cinnamon and 1 teaspoon ground nutmeg. Make sure you sprinkle the sugar and spices evenly and completely over the rolled out dough, including the edges.
Working lengthwise, roll the dough into a log, pinching its edges to seal. Cut the roll into 12 pieces, each about 2 inches wide. Place cut sides down on a parchment-lined 18 x 12 inch jelly roll sheet pan, spaced 3/4 inches apart. Cover with plastic wrap and let rise in a warm place until the edges of the roll are rounded and touching, about 1 1/2 to 2 hours.
Once the rolls have risen, preheat the oven to 350 (F). Bake the rolls in the preheated oven for around 25 to 30 minutes, or until the edges of each bun are golden in color. Let cool on a wire rack. While the rolls are cooling, make the rum icing. Combine 3 ounces softened cream cheese, 2 tablespoons eggnog, 1 tablespoon milk and 1 tablespoon dark rum in the bowl of a freestanding electric mixer fitted with a paddle attachment and beat on a low speed until combined. Add 1 1/2 cups confectioners' sugar all at once and beat until fluffy and of drizzling consistency. Use immediately to drizzle on top of each cinnamon roll while the rolls are still warm, using a rubber spatula or an offset spatula to spread out the glaze.