Partially melt ½ cup salted butter in the microwave for 10 to 15 seconds, then use a pastry brush to stir in 1 tablespoon vanilla bean paste and brush the butter mixture all over the surface of the dough. Yes, we are partially melting already room temperature butter because this allows us to do a quick partial melt and stir the butter into a creamy paste-like consistency for brushing. You don't want to use all melted butter for this step because it's too thin and won't hold the filling in as well.
In a medium bowl, stir together 1 cup dark brown sugar, 2 tablespoons corn starch, 2 tablespoons ground cinnamon, ¼ teaspoon ground nutmeg, ¼ teaspoon salt with a fork until mixed.
Sprinkle the cinnamon sugar mixture over the butter, and use your hands to spread the mixture evenly over the dough, leaving a ½-inch border at one of the longer ends. Then, use a rolling pin to roll over the filling, or use your palms to press the sugar filling into the dough.
Use a pizza or pastry cutter to cut the dough into 12 strips about 1½-inch wide, with the cuts starting from the longer (18-inch) side of the dough.
Roll up each strip of dough to create a pinwheel, starting with the fully sugared end, making sure it's fairly tight, then securing with the exposed buttered end without sugar on it. You can brush more butter onto the outside of the roll if needed to secure the end.
Place the rolls on the parchment-lined baking pan with a little space between.
Pour ¾ cup eggnog over the top of the cinnamon rolls right before covering for their second rise, about 1 tablespoon over each roll. (You can skip this step if desired and carry on with the recipe with no additional changes).
Cover the rolls with plastic wrap and allow to rise for 20 to 30 minutes before baking; they won't quite double in size. Preheat the oven to 350°F while the rolls undergo their second rise; this ensures the rolls can be placed directly into the oven when they are done and will not overproof while waiting for the oven to heat up.
Bake the rolls on the lowest rack of the oven for 18 to 22 minutes or until golden brown. When done, the center of the rolls should read 190°F on an instant-read thermometer. Transfer the pan to a wire rack to cool.
Overnight Bake: You can also place the rolls in the fridge overnight to do a cold proof for the second rise. Preheat the oven to 350℉ and remove the rolls from the fridge 10 minutes before baking. Overnight rolls may require an additional 5 minutes of baking time.