In a small saucepan heat sour cream, 4 Tbsp sugar, 2 Tbsp butter and 1 tsp salt. Stir till melted and combined. Turn off heat and let cool to 110° or below.
In a small bowl or glass measuring cup mix yeast with ¼ cup warm water plus 1 Tbsp sugar. Stir until dissolved and let sit, for about 5 minutes, until foamy.
In the bowl of a stand mixer beat the cooled sour cream mixture with the yeast mixture. Add egg and 1 cup flour mixing to incorporate. Reduce speed to low and gradually add remaining 2 cups of flour. The dough should start to become soft and form a ball, still slightly sticky and not too dry or dense. If it is too sticky add more flour 1 Tbsp at a time.
Turn dough out onto a lightly floured surface. Knead for about 10 minutes until smooth and elastic.
Butter the sides of a large glass bowl and place the dough inside, turning to cover dough in butter. Cover the bowl with a tea towel and let it rise in a warm place for about an hour or until dough doubles in size.
After dough has risen for an hour punch it down. Then roll out into a 22" x 12" rectangle. Spread the 5 Tbsp softened butter evenly over the dough leaving about 1" un-buttered around the edge. Stir together ¼ cup brown sugar and cinnamon, and sprinkle evenly over butter.
Here's the OPTION part: I braid my dough, but you don's need to do that. You can just roll it up and bake in the oven as a single roll. I will give you both methods.