Make the dough. In the bowl of a stand mixer, dissolve the yeast in ½ cup of the warm milk and mix with 1 tablespoon of the sugar. Let sit until foamy and bubbling, around 10 minutes.

Add the rest of the milk, the remaining sugar, the eggs, the vegetable oil and the vanilla and salt to the bowl. Mix with a whisk attachment to combine.

Add the flour to the bowl and mix until smooth on medium speed. Switch to a dough hook and knead to make a smooth, soft dough, adding in the butter one piece at a time as it kneads, around 5-7 minutes. When finished, the dough will be smooth, slack and very wet. 

Place the dough in a well-greased bowl, cover and let rise for 30 minutes on the counter. Place in the refrigerator, covered, and let rise for another 1 hour.

Make the filling: in a bowl, combine the sugars, cocoa, oil and salt until it resembles wet sand. Set aside.

Assemble the schnecken: on a well-floured counter, roll out the dough into a rectangle about 18 inches wide and 12-15 inches long. Dollop chocolate mixture over the dough and spread it smooth using a spatula or your hands, leaving a ½ inch border around the dough. Roll dough lengthwise into a tight spiral.

Using a very sharp serrated knife, cut the log into 1 1/2-inch buns. Arrange the buns cut side up on a baking paper covered sheet pan, leaving at least 2 inches of space between each bun. Brush tops of buns and tops of sides with the egg wash. Leave at room temperature to proof for another 15 minutes, until puffed a bit.

Heat the oven to 350 degrees F. Bake the buns for 20-25 minutes, until lightly browned and the buns have an internal temperature of 190 degrees F. Let cool 10 minutes before glazing. 

To glaze: whisk ingredients together until smooth. Drizzle over the buns. Serve warm.