Combine the buttermilk, eggs, butter, sugar, 4 cups of the flour, salt, and yeast in the bowl of a stand mixer fitted with a dough hook and begin kneading.

Gradually add the remaining 1/2 cup flour as needed to get a sticky, smooth dough that cleans the sides but remains stuck to the bottom of the bowl as it kneads.

Knead for 5-6 minutes, or until you get a nice, smooth dough ball.

Oil a large mixing bowl and transfer the dough ball to that. Cover with plastic wrap and move to a warm, draft-free location to rise until doubled in size. (I usually set my oven to the lowest temperature, let it warm up to about 100-110 degrees Fahrenheit, turn the heat off, the light on, and let the dough rise in there with the oven door closed all the way.)

Once the dough has doubled in size (1 1/2 to 2 hours, depending on how warm your house is), flour your work surface and dump the dough ball onto it. Butter two 8-inch cake pans and set aside.

Divide the dough in half, set one half aside, and roll out the other half with a floured rolling pin until you get a rectangle about 10" by 18".

Drizzle half the melted butter over the rectangle and spread it out with a pastry brush until the entire surface is covered.

In a small bowl, combine the brown sugar and cinnamon. Sprinkle half the cinnamon sugar over the rectangle.

Sprinkle half the chocolate chips over that. Press in gently by running the rolling pin over the filling.

Fold in half, gathering the two long sides together.

Cut into 1-1/2" strips with a very sharp knife. Press down a little to set the filling, then take one strip and twist it so you get a ribbon of cinnamon along the length of it.

Coil the first strip and place it in the center of one of the prepared cake pans.

Twist the next strip and wrap it around the coil in the center of the cake pan, pinching the edges to seal them. Repeat with the rest of the strips until the cake pan is full.

Repeat with the 2nd half of the dough and 2nd cake pan.

Cover with plastic wrap and let rise in a warm place for 30 minutes.

Preheat oven to 375 degrees Fahrenheit.

Remove plastic and bake on the center rack in the preheated oven for 23-25 minutes, or until springy to the touch and lightly browned.

Remove from oven, place plates over the tops of the pans and invert, transferring the cakes onto the plates. (If you do not do this immediately, the cakes will get stuck in the pans like glue. Not that I'd know anything about that...)

While the bun cakes are baking, prepare the frosting.

In a large mixing bowl, combine the frosting ingredients. Beat with an electric mixer until light and fluffy.

Spread half the frosting over each cake while still warm from the oven.

Serve warm or room temperature.