Step 1
1. Mix the dough: In a large bowl, combine the bread flour, milk, sugar (or honey), salt, active sourdough starter, egg + yolk, vanilla, and 1/2 tsp cinnamon. Mix until ingredients are just combined. Cover and rest 20 minutes (autolyse).
Step 2
2. Knead and add butter: Knead the dough until slightly elastic. Gradually incorporate the 90 g softened butter, adding a bit at a time and kneading between additions, until the dough is smooth, soft, and well-developed (about 8–15 minutes of kneading total by hand or in a mixer).
Step 3
3. Bulk rise: Place dough in a lightly oiled bowl, cover, and ferment at room temperature for 4–6 hours, or until it has increased about 35–40% in volume (timing will depend on starter activity and room temperature).
Step 4
4. Cold proof (overnight): Transfer the covered dough to the refrigerator and cold proof overnight (about 8–14 hours) to develop flavor and make handling easier.
Step 5
5. Prepare filling: While dough is resting or before shaping, mix the filling ingredients — 220 g room-temperature butter, 230 g sugar, and 4–5 tbsp cinnamon — until smooth and spreadable. Keep at room temperature.
Step 6
6. Shape: Remove dough from the fridge and let sit ~10 minutes to take the chill off. On a buttered (or lightly floured) surface, roll the dough into a large rectangle.
Step 7
7. Fill and cut: Spread the cinnamon-sugar filling evenly over the rolled dough. Cut the filled dough into small squares (or strips then squares) sized to fit standing upright in a loaf pan — aim for pieces that will create pull-apart layers when stacked.
Step 8
8. Arrange in pans: Line two standard loaf pans with parchment. Stand the cut squares upright and place them snugly, side-by-side, in the pans so they form layered stacks.
Step 9
9. Final proof: Cover the pans and let the loaves proof for 2–3 hours at room temperature, until puffed and roughly doubled.
Step 10
10. Bake: Preheat oven to 320°F (160°C). Bake the loaves for 30–35 minutes, or until the tops are golden and a skewer inserted into the center comes out clean or with only a few moist crumbs. If tops brown too quickly, tent lightly with foil.
Step 11
11. Make frosting: While the loaves cool slightly, beat the frosting ingredients — 170 g cream cheese, 7 tbsp butter, 1 tsp vanilla, and 1 1/2 cups powdered sugar — until light and fluffy.
Step 12
12. Finish: Remove loaves from pans and cool a bit on a rack. Spoon or spread the cream cheese frosting over the warm (not piping hot) loaves so it melts into the layers for a gooey finish. Serve warm or at room temperature.