For the dough: Activate the yeast by adding it to a mixer bowl with 2 cups warm water and 1/2 cup of the sugar. Let it sit until it's foamy on top, about 5 minutes. Add the milk, melted butter, sour cream, eggs and remaining 1 1/2 cups sugar. Fit the mixer with the dough hook attachment, then mix on medium speed until well mixed. Add flour and oil and mix until dough starts pulling from the side. Cover with plastic wrap and let it rest for 2 hours.
For the garlic beef "asado:" Whisk together oyster sauce, soy sauce, sugar and hoisin in a bowl until sugar dissolves. Saute onions and garlic in oil in a saucepan over low heat until translucent. Add beef and cook until brown, stirring frequently to prevent onions and garlic from burning. Add sauce mixture and let simmer until beef is tender, about 2 hours. Make a slurry by stirring together cornstarch and 1/2 cup water, then add it to the sauce. Cook until it thickens. Turn off heat and let cool.
Preheat the oven to 350 degrees F.
Portion out the dough into 4-ounce balls on a floured surface and flatten out with a floured rolling pin. Add 4 ounces of the filling and seal into desired shape, then transfer to a baking sheet. Brush with egg wash and let stand for 15 minutes. Give a final brush of egg wash, then bake until golden, about 30 minutes.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.