1. Before you begin: This recipe is written for a 13x4 loaf pan. If you are using a different size, use the calculator above this recipe card for a revised ingredient list. Additionally, a ton of ingredient substitutions have been tested. Please see the substitutions section for tips.

The Night Before

1. Make the stiff sweet starter: In a small jar, mix 30 g sourdough starter, 30 g honey, 60 g water, and 120 g bread flour until it forms a ball. Knead outside of the jar to fully incorporate the ingredients. Cover loosely and let ferment at room temperature until morning.
   
2. Soak your raisins: In a small bowl, combine 100 g raisins with 10 g vanilla extract. Give it a shake and cover until morning. If you forget this step, soak the raisins first thing in the morning, or for at least 30 minutes.

Bake Day

1. Make the tangzhong: Mix 35 g bread flour and 175 g milk in a microwave-safe bowl. Microwave in 30-second intervals, stirring between each, until thickened and reaches 150°F (65°C). For me, it usually takes 3-5 rounds to finish. Let rest on the counter for about 30 minutes, or until the mixture has cooled down to below 100°F (38°C).

   Note: you can also do this the night before and refrigerate the tangzhong overnight.
   
2. Mix the dough: In stand mixer bowl, combine All of the stiff sweet starter, All of the tangzhong, 195 g cool water, 40 g sugar, 45 g avocado oil, 515 g high-protein bread flour, and 12 g salt. Mix on a low speed for 1-2 minutes until ingredients come together, then increase to a medium-low speed and mix until dough reaches at least a weak windowpane. It takes about 7 minutes in the Ooni Halo Pro, 10 minutes in a Bosch and upwards of 15-20 minutes in a KitchenAid, for reference. Please see the Notes section at the bottom for hand mixing instructions.
3. The dough will feel slightly tacky after mixing, but it should hold its shape and have a soft texture when you poke it. If the dough still feels loose and overly sticky after several minutes of mixing, add additional flour in 1 tbsp increments, but please be sparing, or you'll end up with a dense loaf.
4. Add your soaked raisins to the stand mixer and mix on low speed for 1-2 minutes, or just until the raisins are fully incorporated into the dough.
   
5. Bulk fermentation: Transfer to lightly oiled bowl, cover, and let rise in a warm place (80-85°F/27-29°C) until risen by about 30% and small bubbles appear around the sides of the bowl (about 3-5 hours).
   
6. Prepare filling: In a small bowl, whisk together 1 egg with 1 tsp water. In a separate bowl, combine 5 tbsp brown sugar, 2 tbsp bread flour, and 1 tbsp cinnamon.
7. Shape the dough: Spritz your loaf pan with a nonstick oil spray. Dump dough onto a lightly floured work surface. Using a rolling pin, roll dough into a long rectangle slightly narrower than pan width (about 10" wide by 21" long). Try to pop large bubbles as you roll. Brush the dough with your egg wash and evenly sprinkle the cinnamon sugar mixture over the egg wash, smoothing it out with your hands.
   
8. Roll up the dough tightly, pinching the seams on the ends as you roll to keep the cinnamon sugar mixture inside. Place your dough log seam-side down in loaf pan. Use a toothpick to pop any bubbles on the surface of the dough.
9. Second rise: Cover with plastic wrap and let rise in your warm spot until very puffy and the dough is even with the height of the pan rim (approximately 3-5 hours).
   
10. Bake: Preheat oven to 350°F (175°C). Bake uncovered 45-50 minutes until internal temperature reaches 200-205°F (93-96°C). See Notes for different loaf pan size bake times. If the top of the loaf is getting too dark, cover with foil. Once done, immediately brush hot loaf with 1 tbsp butter. Cool in pan 5-10 minutes, then turn out onto rack. Cool completely before slicing (1-2 hours).