German Butter Cake

Base:

1. In a small bowl, stir together milk, vanilla, and yeast, until yeast has dissolved. Set aside.
2. In bowl of a stand mixer fitted with a paddle attachment, mix butter, sugar, and salt together for 2 minutes on medium speed. Add egg and mix for an additional minute, scraping sides of the bowl as necessary. 
3. Turn mixer to low speed and add flour, mixing until combined.
4. Pour in yeast mixture and mix on low speed for 30 seconds.
5. Replace the paddle attachment with a dough hook and turn mixer to medium speed. Mix for 3 minutes. Alternately, knead dough by hand on a lightly floured surface if you don’t have a hook attachment.
6. Transfer dough to a lightly greased bowl. Cover with a clean dishtowel and allow dough to rise in a warm place, until doubled in size, approximately 30 minutes.

Topping

1. Line a 9x13-inch pan with aluminum foil and coat with non-stick spray. Set aside.
2. In a clean bowl of a stand mixer fitted with a paddle attachment, mix  butter and sugar together for 2 minutes until combined. Add vanilla and eggs and mix for another minute, scraping  sides of the bowl as necessary.
3. Turn mixer to low and add flour and milk and mix until combined and smooth.

Assembly:

1. When dough is risen, spread it out to all four edges of the prepared pan. Press dough up sides of the pan.
2. Spread topping mixture onto dough. Cover with a clean dishtowel and allow to sit for 20 more minutes.
3. Preheat the oven to 375°F. 
4. Bake for 30-40 minutes until top is golden but not quite set.
5. Allow cake to cool completely before cutting into bars. Dust with powdered sugar if desired.