Step 1

Add the yeast to 1/4 cup of lukewarm water.

Step 2

Sift the flour into a large mixing bowl.

Step 3

Add the yeast, egg yolks, milk, sugar, vanilla, and salt and stir until you get a sticky smooth dough, about 10 minutes.

Step 4

Transfer to a lightly floured large plastic container with lid, and let it rise for 4 hours.

Step 5

Line a large baking sheet with parchment paper.

Step 6

With lightly oiled hands, form the dough into little ping-pong-sized balls and place on the baking sheet. Cover gently with plastic wrap and let rise in a warm place for an additional 2 hours.

Step 7

Preheat the oven to 355°F.

Step 8

When doubled in size, brush the buns very gently with the egg whites, covering the entire surface of the buns.

Step 9

Bake for 20 to 22 minutes. Remove and let cool on a wire rack.

Step 10

Measure the cream and powdered sugar into a large bowl and whip with a whisk for about 5 minutes, or until it becomes whipped cream.

Step 11

Slice each bun across the top, fill with fresh whipped cream, and top with additional powdered sugar and the cocoa powder.