In a small bowl, dissolve yeast in 1/2 cup warm water as per package directions for the correct temperature to ensure that you keep your yeast alive (typically between 100-110F).
Heat the eggnog until slightly warm (approximately 30 seconds in microwave).
In a large bowl, mix the eggnog, sugar, melted butter, salt, egg, and ground nutmeg. Add two cups of the flour and mix to combine.
Add in the yeast and stir. Add additional flour, 1/2 cup at a time, until the dough is easy to handle (the amount of flour that you need will vary).
Roll the dough out onto a lightly floured surface and knead for 5 to 10 minutes. (You can knead in a stand mixer as well at speed 1 or 2 as per mixer instructions. I have found a stand mixer takes longer). The dough is ready when you can stretch it thinly to see light through it without it breaking, and the dough bounces back when you press it with your finger.
Place the dough into a greased bowl (you can use 1-2 teaspoons of vegetable oil to coat the bowl you mixed everything in). Cover bowl with saran wrap and then a kitchen towel. Let sit until the dough has doubled in size, approximately 60-90 minutes.
When dough has doubled in size, punch it down. Then put it back on a floured surface and using a rolling pin, roll the dough into a rectangle approximately 15x9 inches.
Spread the 4 Tablespoons of melted butter on top of the dough. Mix the nutmeg, cinnamon, and brown sugar and sprinkle the mixture over the butter. Sprinkle the diced nuts if using on top of the sugar mixture. Use more or less to taste and based on how far your dough was rolled.
From the long edge, tightly roll the dough all the way to the other long edge and pinch dough together to seal.
Using a serrated knife, cut the log in half. (The serrated knife will help prevent the dough from flattening when cutting). Then cut each half into half again so that you have four equal pieces. Lining up two pieces at a time, cut each into three rolls so that you have a total of 12 rolls.
Coat the bottom of your 9x13" baking dish with some additional melted butter and sugar to coat. Place the cinnamon roll slices close together (four rows of three) in the dish and let them rise until the dough has doubled again, approximately 45 minutes. (If you are making these the night before, once the rolls have doubled in size, cover them in plastic wrap and place them in the refrigerator. In the morning, pull them out to warm to room temperature before baking).
Preheat the oven to 350F. Once the rolls have doubled in size, place them in the oven and bake for about 30 minutes or until they are starting to brown.
While the rolls are baking, prepare the icing. Whisk the cream cheese in a stand mixer until creamy. Add the warmed eggnog and whisk in until combined. (It is best if the eggnog is not cold as it can cause the cream cheese to clump up. Warm the eggnog slightly to avoid this in the microwave for approximately 15 seconds). Add the powdered sugar and whisk until smooth. Add more powdered sugar if needed to reach your desired consistency.
When the rolls are done, let them cool slightly and then top with the icing. Serve warm.