Measure sourdough starter into large bowl and mix in yeast, milk, and butter with warm water.
Add all-purpose flour while mixing.
Knead to form dough that is soft and elastic. (I use an electric mixer for 6-8 minutes)
Form dough into two dough balls, and place in two separate greased bowls.
Cover bowls for 4 hours or overnight in refrigerator.
Mix together softened butter, powdered sugar, honey, and vanilla. Set aside.
Once dough doubles, turn it out on a floured work area, working one dough ball at a time.
Roll out a rectangle 12” by 20”. If your dough springs back somewhat, let it rest for 5 minutes.
Spread butter mixture across top of rectangle dough surface.
Sprinkle with granulated sugar and cinnamon.
Cut three horizontal strips of dough.
Stack all three strips on top of each other, cutting into squares.
Place dough squares in 9” by 5” bread pan lined with parchment and turned on its side for an easier placement.
Turn bread pan upright. Cover with cloth for 2 hours in warm kitchen
Bake at 375℉ for 25 minutes uncovered and cover for additional 10 minutes.
Remove from oven and let cool.
Combine powdered sugar and milk to form glaze. Drizzle over cooled bread.