Authentic German Butter Cake (Butterkuchen)

INGREDIENTS

For the Sponge:

4 1/2 cups

all-purpose flour, divided

1 1/2 oz

fresh yeast or 1 package dry yeast (2 1/2 teaspoons)

1 cup

lukewarm milk (110 F)

sugar

For the Yeast Cake:

1/2 tsp

salt

large room-temperature egg

8 oz

room-temperature butter, divided

1 1/4 cups

sugar, divided

2 tsp

cinnamon