While the buns are proofing, divide the dough for the topping into 12 pieces (about 27 to 29 grams each). Roll each piece into a ball.
Take a plastic storage bag, and cut off the zipper. Continue cutting the bag along the edges so that you have 2 large sheets of plastic. You’ll be rolling the topping in between these plastic sheets.
In a small bowl, prepare the egg wash by whisking an egg yolk with 1 tablespoon of milk.
After the buns are done proofing, start rolling out the topping.
Take a ball of the topping dough and place it on the center of a plastic sheet. Lightly flatten the dough out with the palm of your hand. Then, cover the flattened disc with the other sheet of plastic. Roll out the dough until you get a circle that is 3.5 to 3.75 inches wide.
Peel off the top sheet of plastic, turn the topping onto your hand and carefully peel off the other sheet of plastic.
Drape the topping over one of the buns. The topping shouldn’t cover the bun completely. The topping can burn if it touches the bottom of the baking sheet. Continue rolling out the topping and draping it over the buns.
Brush the tops of the buns with egg wash.
Bake the buns for 14 to 16 minutes, until the tops are lightly golden.
Once the first batch of buns is in the oven, prepare the second batch of buns and bake.
Let the buns cool on the baking sheet for several minutes before transferring them to a cooling rack.
Enjoy the buns while they’re still warm! That’s when they are the tastiest.