Make the stiff sweet starter: In a small jar, mix 15 g sourdough starter, 15 g honey, 30 g water, and 60 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.

Make the tangzhong: Mix 35 g bread flour and 175 g whole milk in a microwave-safe bowl. Microwave in 30-second intervals, stirring between each, until thickened and reaches 150°F (65°C). Cover and refrigerate until morning.

Mix the dough: In stand mixer bowl, combine All of the stiff sweet starter, All of the tangzhong, 225 g cold water, 75 g honey, 25 g avocado oil, 575 g high-protein bread flour, and 12 g salt. Mix on speed 1 for 1-2 minutes until ingredients come together, then increase to speed 2 and mix for 10-15 minutes, or until dough reaches a weak windowpane.

Bulk fermentation: Transfer to lightly oiled bowl, cover, and let rise on counter until evening (8-12 hours).

Shape the dough: If not using a nonstick bread pan, lightly oil it. Bring dough out of the fridge if you had to slow fermentation because you did not have time to bake it and let it raise and bake on the same day and turn it onto work surface. Using a rolling pin, roll dough into rectangle slightly narrower than pan width. Roll up the dough tightly, pinch the seams on each end, and place your dough log seam-side down in bread pan.

Second rise: Cover and let rise on the counter, overnight, until very puffy and the dough is even with the height of the pan rim (approximately 8-12 hours).

Bake: Preheat oven to 350°F (175°C). Bake uncovered 40-45 minutes until internal temperature reaches 200-205°F (93-96°C). 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).