For the Dough:

1. Warm the buttermilk in the microwave Whisk together the buttermilk, sugar, and molasses in a heat-safe glass measuring cup (you can also do this in a small pan on the stove). Microwave in 15-20 second increments until the temperature reads between 100-110°F on an instant-read thermometer – you do not want it any hotter than 115°F or it will kill the yeast.
2. Sprinkle the yeast over the surface of the milk and allow it to sit until foamy, about 5 minutes.
3. Pour the mixture into the bowl of a stand mixer and then add in the egg, egg yolk, and melted butter. Whisk to combine.
4. Stir in the flour, spices, and salt and mix with the dough hook until a thick, shaggy, and somewhat sticky dough forms (alternatively, this can be done by hand).
5. Lightly flour your countertop and turn the dough out from the bowl. Knead the dough for a few minutes with your hands until it is elastic and smooth.
6. Place the kneaded dough ball into a greased bowl.
7. Cover the bowl and set in a warm place to rise for 1 hour or until it has doubled in size.

For the Filling:

1. Whisk together the softened butter, molasses, and vanilla until smooth.
2. Stir in the sugar, spices, and salt and mix until well combined.

To Assemble:

1. Place the dough on a lightly floured surface and roll it out thinly to a rectangular shape, roughly 12 x 16 inches.
2. Spread the filling all over the surface of the dough, leaving a ½-inch border around the edges.
3. Working from the longer end of the dough, tightly roll to form a log shape.
4. Butter a 9 x 13-inch baking dish. Slice the log into 12 equal pieces and place them, cut side up, in the buttered baking dish.
5. Cover the rolls with a towel and allow them to rest for another 30 minutes (at this point, you can also refrigerate the rolls overnight to use the next day. See recipe notes). During the second rise time, preheat your oven to 375°F.
6. Once the rolls have risen enough so that they are all touching in the pan, transfer the pan to the oven and bake for 20-25 minutes or until the rolls are puffed and golden brown.

For the Frosting:

1. While the rolls are baking, make the frosting by creaming together the cream cheese and butter until smooth and creamy. Add in the vanilla.
2. Stir in the powdered sugar and beat again to incorporate. Add more powdered sugar, as needed, to reach desired thickness. If the frosting gets too thick, add a splash of milk.
3. Spread the frosting all over the rolls while they are warm. Serve!