Combine yeast, warm water & sugar in mixing bowl. Stir gently once, then let sit until yeast has proofed & mixture is foamy.
Heat sour cream in microwave for 30 seconds. Add to yeast mixture, along with the egg, vegetable oil, and vanilla. Mix for about 1 minute before adding in flour and salt and then mixing until dough comes together. I like about a quarter sized amount of dough to be sticking on the very bottom. If your dough looks a bit dry, add 1 TBSP warm water.
Once you've achieved a good consistency, mix the dough on low for about 6-7 minutes. (Or knead by hand about 10 minutes.) Proper kneading is critical to great textured homemade bread!
Once dough is done kneading, cover and let rise in a warm place for about 1 hour; until dough has doubled in size.
Punch dough down and knead several times. Divide dough into 3 equal sections. Roll each section into a rope about 1.5" in diameter and roughly 15" long.
Brush each rope with melted butter. Combine sugar and cinnamon in a bowl. Stir until cinnamon is well incorporated. Set aside about 2 TBSP and sprinkle half onto each rope. Turn ropes over and repeat on the other side.
Assemble ropes close together and press the ends together. Braid the ropes. Brush a round Springform Pan OR jelly roll pan/ sheet pan with butter. Transfer braid to the pan, curling the braid around itself in a circular motion. Tuck the end under. Sprinkle with remaining cinnamon sugar. Place dough back in the warm spot and let it rise for another 30-45 minutes.
Preheat the oven to 350 degrees F. Bake dough for about 25 minutes- until top is golden brown. Let cool about an hour.
Whisk powdered sugar and hot water together. Drizzle over cinnamon roll bread. Cut into wedges and serve.