Mix together yeast, sugar, and lukewarm milk and set aside for 5-10 minutes until the yeast is foamy. If the yeast does not foam, it may be inactive. Try again with new yeast.
In bowl of stand mixer with dough hook attachment, combine flour, egg, milk and yeast mixture, 1/2 cup of tangzhong starter, and salt. Mix on medium-low speed until combined. While the stand mixer is running, add pieces of softened cream cheese until fully incorporated. Mix on medium-low speed for another 15 – 20 minutes until dough passes the window pane test. You should be able to stretch the dough quite thin. If it does not pass the window pane test, keep kneading and check again.
Shape the dough into a ball and placed into a lightly greased bowl. Cover with plastic wrap and let proof for 45 - 60 minutes until doubled in size.
Grease a 9 x 13 in. baking pan. Lightly flour a work surface and turn the dough onto the surface. Knead a couple of times to squeeze out the air bubbles. Divide the dough into 12 even pieces and shape each piece into a ball. If the dough is sticky, sprinkle a bit of flour and flour your hands as well. Place the balls in the baking pan.
Cover the baking pan with plastic wrap and let proof for another 45 minutes. When you press your finger into the dough, the indent should come back halfway. If it comes back all the way, it needs more time. Towards the end of the proof, preheat your oven to 350°F.
Brush the tops of the rolls with milk. Place in the center rack and bake for 25 minutes until golden brown and makes a hollow noise when tapped.
Remove from the oven and let cool for 15 - 20 minutes before removing from the pan. Sprinkle with powdered sugar if desired and enjoy fresh!