Make the Dough:

1. Place the buttermilk and softened butter, and 1 Tbsp of the sugar into a microwave-safe bowl, and, using 20-second intervals, heat to the temperature it advises on your yeast packet. You can test this with a thermometer, or insert your finger, and since this is close to body temperature, 105F should feel ever-so-slightly warm, and 120 should feel definitely warm. Place the warm buttermilk mixture into the bowl of a stand mixer and whisk in the yeast. Cover and let sit for 5-10 minutes. After this time, there should be some bubbling and foaming. That lets you know you can proceed to the next steps.
2. Using the paddle attachment, at Medium-Low speed, add in the rest of the sugar, the salt, eggs, vanilla, flour, and cardamom. Mix until the flour is incorporated, then remove the paddle attachment, replacing it with the dough hook. (See Note 2) Knead 7-9 minutes, or until the dough is smooth, elastic, and a bit sticky. It should be pulled away from the bowl, leaving the sides of the bowl pretty clean, and should also stick to the bottom of the bowl. It should feel “tacky” but not stick to your finger so that it doesn’t come off cleanly when pulled. If it is too sticky, add a bit more flour – maybe 1/4-1/2 cup, and knead another minute or two.
3. Place a teaspoon or two of neutral oil in a large bowl, form the bowl into a ball, and place it in the bowl. Cover with a damp towel and place in a warm spot to rise. If your oven has a low setting (150F or lower), you could preheat it to that temperature, then turn the oven off and place the covered dough inside. Leave the dough in the warm spot until it doubles in size, 1-2 hours. While the dough rises, make the filling.

Make the Filling:

1. In a Medium bowl, whisk together the sugars, cinnamon, and cornstarch.
2. Cut the apples (peel if you like – I didn’t) into very small, thin sections. No more than 1/4” thick, and 1/2”x1/2”. This will enable them to fully cook during the short bake time.
3. On a large, flour-covered surface, roll the dough into a large rectangle, about 18-20 inches wide and 14-15 inches deep. Spread the softened butter over the entire surface.
4. Sprinkle the cinnamon mixture over the butter.
5. Scatter the apple pieces over the cinnamon mixture.
6. Starting at the long side of the rectangle, roll the dough as tightly as you can, into a log, being careful not to stretch the dough. Take your time, this can be difficult but is worth the patience! Brush a little egg wash (1 egg + 1 Tbsp water) over the far edge to seal the cylinder of dough. 
7. Using a sharp knife, mark the halfway point of the dough with a small, shallow slice. Then divide each half, using similar shallow slices, into halves, then halves again, then one more time, so you have 16 roughly equal slices. Then complete the slices so you have 16 discs of even thickness.
8. Place 12 of the round slices into a parchment lined, or buttered 9×13 pan, and 4 into an 8×8 pan. Alternatively, you could use 2-9×9 pans or 2 round pie or cake pans. Cover the pans with a damp cloth and place them in a warm spot for 20-40 minutes, until they have doubled in size. During this time, preheat the oven to 350F (or 330F for Convection). Brush tops of rolls with the 1/3 cup cream. Place risen rolls into the oven and bake until golden brown. If you don’t want them too brown, cover lightly with foil after 12-15 minutes. Bake 20-25 minutes. Mine took 20 minutes to be done to my liking. Remove from oven to cool.

Make the Maple topping:

1. Mix all of the topping ingredients together until smooth.
2. Spread over rolls that are cooled completely, or, if you are serving immediately, wait at least 15 minutes to glaze and serve.