In a small bowl, combine yeast, powdered sugar, and 2 tablespoons of the warm milk. Stir well and let stand for about 15-20 minutes until foamy and thick.
Make the Dough
In a bowl, beat the eggs and measure out 5 tablespoons. Reserve the remaining beaten eggs to make the yema.
In a large bowl, combine sugar and the 5 tablespoons of eggs. Stir until sugar is incorporated.
Add the remaining warm milk, the yeast, and 1/4 cup of the flour. Stir mixture until smooth and let stand briefly for about 2-3 minutes.
Combine the remaining flour and salt and add to the bowl. Stir with a wooden spoon for 7 minutes or until it has gathered into a smooth and shiny dough. This dough will be very sticky. Do not add any flour.
Add 2 tablespoons of the warm, melted butter and using your hands, mix the butter into the dough. Mix for about 5 minutes, incorporating the butter into the dough until it is soft, smooth and very shiny.
Place dough in a lightly greased bowl and let rise for 1 1/2 hours or until doubled in bulk.
Knead the dough briefly just to deflate. Place it back in the bowl and chill in the fridge for one hour.
Make the Yema filling:
In a saucepan over medium, combine potato and enough water to cover. Bring to a boil and cook until very tender.
Drain the potatoes and mash with the 4 teaspoons of milk until smooth. Set aside.
In a medium saucepan over medium heat, add condensed milk, 4 tablespoons of the mashed potato, and the remaining egg from the dough ingredients.
Stir the mixture constantly until thick and spreadable, about 15 minutes. Allow to cool.
Assemble the Yema Bread Rolls
Grease a 9 inch round pan with melted butter. Set aside.
Deflate the dough by lightly kneading and divide into 15 portions. Lightly flour your hands and work surface as needed.
Roll each portion into a smooth ball and then flatten with your palms until it is about 1/4 inch thick.
Spoon about half a tablespoon of the yema filling on the center of the flattened dough. Fold and stretch the edges of the dough over the filling, then pinch the end while twisting it slightly to seal. Repeat with the other portions.
Arrange the filled dough on the greased baking pan seam side down. Space them close to one another.
Brush with the remaining melted butter and cover with a lightly buttered plastic wrap. Let rise for 1 1/2 hours.
Place your rack in the lowest position inside the oven. Preheat oven to 400 F.
Set the baking pan on a baking sheet and place in the oven.
Bake for 5 minutes, then lower temperature to 375 F. Bake for another 15 minutes or until the top of the buns are nicely golden.
When assembling the buns, keep the filling in the center of the dough and leave about 1/2 inch border as any smears on the sides will make sealing the dough difficult.