I used Greek plain yogurt mixed with milk instead of sour cream for this one. The result is just as good.
20 oz of flour divided up to: 10 oz, 6 oz, 4 oz
Whisk in mixer's bowl 4 large egg yolks and 1 whole lage egg, 3/4 cup sour cream ( my preference ) or buttermilk or 1/2 C yogurt plus milk to make 3/4 C, 4 oz organic sugar cane. Then add 10 oz of flour that is mixed with 9 oz of instant dry Yeast and 1-1/4 tsp Kosher Salt. Use spatula to mix well. Connect to mixer and add 6 oz of flour. Hand mix in then use dough hook to knead. If you love your mixer, I strongly suggest hand mix dry flour in first then use the mixer. This will prevent dry ingredients to eventually clog the motor housing and cause to loose power, etc. Knead for 5 min at your mixer's allowed speed for kneading. At slow speed, slowly add extra flour 1 Tbsp at a time (out of remaining 4 oz). Knead at regular speed for another 5 min, adding flour 1TBsp at a time until the dough leaves the sides of the bowl. Transfer to work surface and knead 10 times and form into a smooth ball. Turn it over in a greased bowl. Cover to proof till double in size. You can make the dough a night before, too,
If you started forming dough at night, roll the dough out, spread 2 to 3 Tbsp of softened butter across the rolled dough. Spread brown sugar 1 to 2 C and 2 Tbsp Ceylon Cinnamon across. Sprinkle poppy seeds as much you like.
Start rolling the dough. Roll up just tight enough - not too tight or not too loose that fillings would drop out when the cut piece is placed in baking pan upright.
Line a cake pan with rim with parchment paper.
Use serrated knife and slice. *18 slices for 9x13 or 12 for large tall size - use brownie pan. Place the sliced ends in center and start filling the baking panfrom center out. Cover the pan with plastic slightly sprayed with vegalene and a air tight lid and refrigerate over night, if desired. Take it out 1 to 2 hours ahead to complete the rising. Preheat oven to 350'F. Cover with Foil and bake for 15 minutes. Prepare frosting - 1/2 C powder sugar + 1/2 tsp milk. Adjust consistency by adding more powder sugar or milk. Remove the foil and bake 10 more minutes.....depending on the size of the slices. Use baker's thermometer to check dough's temp for doness. I am not looking for browning on the top. If you do, your rolls texture will be 'dry'. If the dough at center reads at least 185'F, depending on your oven's BTU, it's done. Remove from oven and drizzle with frosting, if you wish. Enjoy!