Activate yeast: To the bowl of your mixer add the yeast, the 1 tbsp of sugar and the warm milk. Gently whisk it all together and allow it to rest for 10 to 15 minutes. After this time, if the yeast is good, it will froth.
Make dough: Add the butter, sugar, egg yolks, salt, and flour to the yeast mixture. Mix with the dough hook on low speed, until it's all incorporated. Increase to medium high speed and knead for another 5 minutes. The dough should be slightly sticky but still soft to the touch.
First rise: Place the dough in a lightly greased bowl, or the bowl from your mixer and cover it with plastic wrap. Let it rise until it doubles in size, about 45 minutes to an hour. See notes for rising.
Prepare baking dish: I normally use a 9x13 inch baking dish for these, so lightly grease your baking dish with cooking spray or butter.
Form rolls: Dust your work surface with a little flour, place the dough then press it down so that it deflates. Shape it into a ball. No need for additional kneading. Divide the dough in 16 equal pieces. To shape each piece into a roll, take a piece and flatten it with your palm or fingers. Fold it up into a ball by pinching the sides together, turn it over and roll it briefly. See video. Place the roll with the smooth side up onto the prepared baking sheet. Repeat with remaining dough pieces.
Second rise: Cover the pan with plastic wrap or a clean kitchen towel and let the dough rise again until it's doubled in size, another 30 minutes or so.
Prepare oven: Preheat the oven to 375 F degrees.
Brush rolls with eggs: Remove the plastic wrap or kitchen towel and brush the rolls with the egg white, so that they end up nice and shiny. Sprinkle with poppy seeds or sesame seeds, if preferred.
Bake: Bake the rolls for 30 minutes or until golden brown.